On a beautiful day at the marina, Brianna, a teenager in her bikini, suns herself on the deck of a large sailboat. Hearing some thumping coming from down below, Brianna assumes it's her friends in the cabin beneath, noting to herself how they can't keep their hands off each other. The couple, Keith and Carly, approach from the cabin to confess that they weren't doing anything as Brianna notices that the thumping hasn't stopped. She peers over the side of the boat and gasps as she spots the bloated corpse of a man, facedown, bumping in the tide against the boat.
At the station, Jim Longworth strides in looking for Sanchez when he notices Callie, sitting on a lab table, studying a series of x-rays on a light board in front of her. It's an awkward moment as Longworth mentions Callie usually only comes by the office to say hi. Just then Sanchez enters with additional x-rays, making things more awkward. Callie explains that Sanchez is tutoring her for an upcoming test and Sanchez invites Longworth to join them. Longworth declines, but not before correcting Callie on the answer to one of her test questions. They both shoot him a look as Manus enters, explaining that they've just gotten a call from Marine Patrol Services about a floater ID'd as Johnny Hasker, the nephew of Big Jack Hasker. Longworth hasn't heard of either man and Sanchez explains that ten years ago Jack Hasker, his son Hal and nephew Johnny found the shipwreck of a Spanish galleon named the Granada and pulled up a four-hundred million dollar treasure, the biggest ever recovered in the US - and a good reason he might be dead, Longworth notes.
Later on at the marina, Longworth and Sanchez chat about Callie as they head to the crime scene. Longworth laments that Callie usually stops by to say hello if she's in the building. Sanchez tells him next time he should be mindful to not use one of Callie's old friendships to catch a killer. Longworth retorts that maybe next time the killer won't be one of her friends, though he agrees he could have handled the situation better.
They reach the deceased, Johnny Hasker, who has been pierced through the chest with a very old-looking knife. Sanchez quickly sums up that the "weird ass knife" is the cause of death as Longworth looks across the marina to a second crime scene aboard Johnny's yacht. Sanchez explains that based on the bloating and the tide cycle that carried Johnny from his yacht to the neighboring boat, he'd been in the water maybe 12 hours which puts the time of death at around 3am.
As they board Johnny's yacht, Longworth notes that it's not much of a boat for a guy who discovered four hundred million dollars worth of treasure. Sanchez explains that the Haskers fought the Spanish government for ownership of the treasure and only ended up getting to keep a third of it, with Spain taking another third and the rest being divided up by lawyers for both governments. As Sanchez talks, Longworth follows a trail of blood spatter from the rail of the yacht to the deck and into the cabin. It appears that Johnny got stabbed in the cabin, staggered out and then tumbled over the side of the boat into the water.
The men enter the boat's cabin to find a decorated space full of undersea artifacts including a pitted conquistador's helmet, a compass and a small telescope. They observe the ripped couch cushions, scattered papers, yanked-out drawers and blood spatter on the walls. Longworth eyes a melted candle in the center of the dinner table and remarks that it seems like someone's idea of a romantic evening that went south. He drifts over to the ship's controls, noticing that the GPS has been left on and scans through the graphic menu, looking for somethingSanchez speculates that maybe Johnny walked in on a robbery, but Longworth wonders why the killer would erase Johnny's GPS if he was only after money. Sanchez retorts that someone clearly did not want anyone to know where Johnny had been. Longworth adds that maybe where he'd been suggests maybe he was on to something worth killing for.
Later at the marina, Longworth and Sanchez discuss the Haskers and their discovery of the Granada. Longworth mentions how much it must have sucked for the Haskers having to give away two-thirds of the Granada's gold to cutthroat lawyers after sinking their life savings into finding it. Sanchez agrees, telling Longworth that Florida is now filled with amateur treasure hunters looking for the next Granada, but so far no one has found anything that has even come close. He continues that Big Jack and Hal have put the majority of their cut into searching for the wreck of the Magdalena, an even bigger sunken treasure, while Johnny took his cut and opened a seafood business.
Johnny Haskers's nautical themed dockside restaurant is an upscale place on the water, deserted but for one elderly couple picking at their food. Longworth speaks to Haskers's business partner, Mark Ellison, who tells him he can't imagine who would've done this since everyone loved Johnny. Longworth asks Ellison if he has any idea how often love is the reason for murder and questions whether anyone was mad "like that" at Johnny, given that he was attacked on his boat during what appears to be a candlelight dinner. Ellison tells Longworth Johnny wasn't seeing anyone that he knew of.
Longworth asks whether Johnny ever regretted leaving treasure hunting for the restaurant business and Ellison tells him Johnny said treasure hunters died old and broke. Longworth remarks that at least with a restaurant you can go broke while you're still young. Ellison tells him it's no secret that the restaurant isn''t doing well and insinuates Longworth thinks he killed Johnny over the dying business. Longworth tells him it's not unheard of, but Ellison says that Johnny's name was the only asset the restaurant had going for them and the only chance he had to see a return on their investment, so he had absolutely no reason to kill him. Longworth agrees but tells Ellison that somebody did indeed kill Johnny. Ellison suggests Longworth talk to Johnny's uncle, Big Jack Hasker, who loved Johnny like a son. The only bad blood, he explains, was between Johnny and his cousin Hal, Big Jack's son.
Hasker Recovery Shipyard is a dock and warehouse that opens out onto the water. Longworth speaks to Hal Hasker who tells him there was no bad blood between him and Johnny; he just didn't like Johnny treading on the family name with his cheesy restaurant.
Just then Big Jack approaches, a little drunk, his eyes red from crying, and tells Longworth that Johnny was a Hasker through and through. He sighs and says he will never forget the way Johnny's eyes shined "as bright as gold" the day they found the Granada. Hal quickly apologizes for his father, explaining he gets a little emotional whenever he talks about Johnny, and takes away a bottle of Scotch that Big Jack has been drinking from. Big Jack laments that he promised his sister he would take care of Johnny and not let him get lost in treasure hunting fever, but now he has let her down.
Longworth questions whether Johnny helped to find the Grenada and Big Jack says he didn't help find it, he found it singlehandedly. Hal makes a move to quiet his dad and Longworth asks if credit for finding the Granada was a bone of contention for him and Johnny. Hal says Johnny just got lucky, but his father counters that actually Johnny got smart. Johnny could read the ocean floor like a book and realized that the debris field, the debris left behind as ships break apart and scatter their wreckage, was actually from the Granada. Big Jack says they worked the field for ten years on the debris before they knew it was the Granada and they'd spent the past three looking for the debris from the Magdalena, a sunken ship said to be worth twice that of the Granada. Big Jack adds that every time he'd go on a dive he'd think of how much easier it would've been if Johnny had been there with them. Longworth adds that it must have felt like a betrayal when Johnny left to start the restaurant business. After neither man responds, he questions where they were around 3:00 a.m. that morning. Big Jack explains Hal was with him the whole night getting a boat ready to go out on a run, but neither has anyone else to alibi him except the other.
Longworth shows the Haskers a photo of the knife that killed Johnny and asks if either has ever seen the knife before. Big Jack says the knife looks like any number of items found in a shipwreck and Hal makes an off-handed remark about Johnny using the artifacts to decorate his cheesy restaurant. Big Jack gets defensive, saying Johnny was like a son to him, but Hal counters that Big Jack only wished Johnny were his son. On a roll, Hal encourages his father to also tell Longworth how he spent all their money trying to find the Magdalena to reclaim his family's good name after Johnny, the "arrogant little bastard" sullied it. Longworth says he knows why Big Jack wouldn't want to give away that detail - because it would make him look guilty for Johnny's murder. Longworth departs, telling the men to call him if they think of anyone with a stronger motive to kill Johnny than themselves.
That night at Callie's, Callie sits with a stack of medical books talking on the phone with Jeff when Longworth arrives. Callie quickly tells Longworth she's busy studying and Longworth explains that he knows she's still mad and wants to apologize. Callie tells him she's not mad about him arresting her friend, she just doesn't have time to deal with their situation right now. He again apologizes and Callie asks what he needs. Obviously looking for her input, Longworth wonders aloud why sane people would risk their lives to become treasure hunters. Callie explains it's more than money, it's about the romance and excitement, noting that countless ships sank off the coast of Florida and that people find artifacts on beaches, in the glades, even in their own backyards, all the time. Taking this in, Longworth asks Callie how she thinks Johnny Hasker would feel if he found the Magdalena? Callie immediately gets excited, pressing Longworth to tell her if Hasker had actually found the ship. Longworth tells her that he's starting to think Johnny had found it because that's what everyone, including his family and business partner, needed to turn each of their businesses around.
Noticing Callie's computer, he sees that she's been Goggling the Magdalena wreck while they've been talking. She explains that Benito Francisco, a rich colonial official, and his young bride, were heading back to Spain with his fortune on the ship he'd named for her when pirate Black Jack Bellamy attacked them in the Florida Keys. Black Jake took off with Francisco's bride and the riches and left the colonial adrift at sea in a lifeboat. Longworth says he's starting to understand the romance Callie is referring to about treasure hunting. Callie continues that Francisco survived the attack and later battled the pirate for the Magdalena treasure, causing both ships to sink to the bottom of the sea.
Finished with her story, Callie tells Longworth he has to go so she can study, but he still has one more question: With all the debris fields, how can a treasure hunter tell if they've actually found a shipwreck? Callie explains that you have to have proof - an item you can verify against a ship's manifest to determine it was actually on the ship when it sank, to serve as a definitive artifact. As he walks to his car, Longworth calls Sanchez to tell him he has a hunch about their murder weapon that he'd like him to check out.
At the station, Sanchez's preliminary autopsy on Johnny Hasker has determined that Johnny was in fact stabbed to death. What stands out, says Sanchez, are bites Johnny received from a blood-sucking midge, nicknamed no-see-ums because you can't see when they bite. Curiously, Johnny's boat was not infested with no-see-ums, the only way he would've gotten so many bites. Sanchez shows Longworth Johnny's ankles, which are swollen, and says he can't close Johnny's file until he figures out what's going on with the bites and the swelling.
Moving to the computer, Sanchez shows Longworth an image of the murder weapon, explaining he had it carbon tested and learned it's a mid 18th century Spanish dagger with a brass-mounted hilt, a crown pommel and a steel blade. Longworth asks about the markings on the hilt and Sanchez reveals it's the Benito Francisco family crest, meaning that the knife came from the shipwreck of the Magdalena and that Johnny was close to finding the treasure. Longworth is sure this means that Johnny was killed by someone who knew he was onto something and wanted the treasure for themselves - the same person who, Longworth fears, will kill anyone else who gets in his way.
Back at the Hasker shipyard, Longworth shows Hal a photo of the knife, chastising him and Big Jack for not recognizing the Francisco seal after so many years of searching. Big Jack confesses of course they recognized the seal, but they lied because if word got out that someone was close to finding the Magdalena, every amateur salvager would've started looking for it, thereby destroying the debris field.
Longworth adds that if Johnny had found the treasure, it would've really pissed the Haskers off. Big Jack counters that Johnny was a Hasker too and that if he found it it would've been the same as them finding it. Longworth isn't buying this and adds that since Johnny's restaurant business was failing it seemed a good time to get back into the treasure hunting game, but it would've looked terrible for the Haskers, who had spend all their money from the Granada trying to get to the Magdalena, if Johnny were to find it first.
Longworth postulates that Hal might have stolen the coordinates to the treasure from Johnny in order to win his father's approval and get respect for finding the ship, but Hal argues that if that's the case then where's the treasure. At the bottom of the ocean, explains Longworth, waiting till Johnny's murder blows over so that Hal can "find" it. Big Jack laughs and says Hal has never found anything in his life. Longworth leaves as the men continue to argue and answers his ringing cell phone. After listening for a moment, he hangs up, noting to himself that another hat has just been thrown into the ring of this strange case.
Manus and Longworth walk together at the station as she explains this "new hat" is a Dulce Mendez, the lawyer representing the government of Spain who took the Haskers to court over ownership of the Granada. Manus explains Mendez is here because she has heard about the Magdalena and has arrived to reclaim it for Spain. Manus adds that according to Johnny Hasker's phone records, he'd called Ms. Mendez three times over the last two weeks.
When Longworth arrives in his office, Mendez, who has been waiting for him, immediately asks where the knife is, informing the detective that Spain is the rightful owner of any and all artifacts recovered from the Magdalena. Longworth tells Mendez that the knife is in evidence awaiting the murder trial of Johnny Hasker whom she called three times last week. When Longworth points out that she didn't register any emotion over word of Johnny's murder, Mendez argues that just because she talked to Johnny on the phone that doesn't make her a suspect.
Just then, Longworth spots something on Mendez's shoulder that interests him. As Longworth stares at her shoulder, Mendez explains that she and Johnny talked because he wanted to let her know about the Magdalena and even showed her the knife he'd found. She continues that Johnny wanted to avoid the red tape that followed the Granada's discovery. Longworth can't concentrate on anything but Mendez's shoulder. Finally he plucks a coarse blond hair off her shoulder, telling her it was driving him nuts. Annoyed, Mendez leaves, demanding full disclosure on all Magdalena updates in the future as she exits.
After she's gone, Manus remarks that Mendez appears to know a lot more than she's saying. Longworth asks where Daniel is, telling Manus he wants him to look into a bar called the Rusty Crab Pot. Manus tells Longworth that Daniel is studying for finals and turns the conversation to Johnny's financials, which are bleak. It turns out Johnny was so broke that he signed his boat and half the restaurant away to his partner, Mark Ellison, and yet Ellison still gave Johnny another hundred grand the next month. Manus questions why this would be and Longworth says Johnny's either a bad businessman or a bad liar.
At the restaurant, Ellison explains he gave Johnny a personal loan, but Longworth counters that it's a lot of money for a loan and questions whether Ellison wasn't stalking Johnny on claim of the Magdalena. Ellison reiterates that Johnny had given up treasure hunting, but Longworth presses him, saying that if Johnny had told Ellison about finding the Magdalena, Ellison's hundred grand would look like a good investment on half a billion in treasure.
When Longworth threatens to go deeper into his finances, Ellison confesses that Johnny had revealed to him that he had found a debris field but needed money to work on the find, which is where the personal loan came in. Longworth questions where the debris field is but Ellison doesn't know and says he wouldn't have any idea where to look. Longworth counters that somebody knows, like whoever erased Johnny's GPS.
At the library, Callie is having trouble concentrating on studying, so she takes out a book on the Magdalena. Later on, she and Longworth pore over it at a bar.
Callie explains that the book is a captain's log that lists all the contents of the ship, but the type of knife that killed Johnny is not among them. This means either a sailor smuggled in the knife or a Johnny Hasker didn't find the debris field from the Magdalena. Noting that most of the sailors were former prisoners (who kept no shortage of concealed weapons) and women were not allowed on the ship, Callie tells Longworth they need to think like a man and preferably a man who knows about criminals, like a cop.
Longworth tells her that as a man and a cop, in order to solve the crime, he would go back to the people behind the mystery and figured out how they're all related, explaining that once you understand someone's profile, it's easy to tell what they're going to do. He uses her as an example, noting that soon she'll remember she's still mad at him and leave in a huff. Callie says she has to go, but not in a huff, and leaves Longworth smiling with the book and the bill.At the lab, Sanchez confirms the dagger is the real deal, but while the knife is old, the Benito Francisco crest was new. He has found traces of polymethyl methacrylate, a compound used in photo engraving, on the knife, noting that someone coated the handle with it and blasted light through a photographic negative of the Francisco crest, meaning the crest on the knife that killed Johnny Hasker was forged.
Longworth briefs Manus on the case, recapping that Johnny didn't find the Magdalena and that the knife was a con job. Manus questions why Johnny would have tried to strike a deal with lawyer Dulce Mendez if he didn't actually find the ship. Longworth considers that maybe he did actually find the debris field but needed an artifact to convince Ellison to front him the money for the rest of the find. Manus says that she has not found any evidence in Johnny's finances that he bought equipment. Sanchez postulates that maybe Johnny was killed by Big Jack and Hal for the coordinates while waiting for the deal with Spain to go through before he really got started. Longworth has another explanation: Mark Ellison, who gave Johnny the hundred grand, wasn't satisfied with a percentage of the treasure and wanted to wait for Johnny to find the whole thing.
Longworth heads to Ellison's beach house, where Ellison explains Longworth is wasting his time if he thinks he killed Johnny and that he's really the victim since he invested a hundred grand into finding the Magdalena and now someone has stolen the coordinates, and therefore the money, that is rightfully his. Longworth reveals that Johnny is really the one who screwed Ellison, since the knife he showed him from the Magdalena was a fake. Ellison is shocked, but Longworth doesn't believe this is the first time he's hearing about the con and postulates that Ellison killed Johnny when he found out he was swindling him. Ellison swears this is the first time he's hearing about the knife being a fake and asks Longworth if he thinks Johnny's coordinates are fake too, a question Longworth has intentionally coaxed out of him. Ellison immediately regrets asking.
On the phone, Longworth tells Manus he's not sure whether Ellison's motive was to steal the coordinates or to get revenge for the money he lost. Manus tells Longworth to keep Ellison in play. She adds that she has gotten the number of the Crab Pot restaurant for Longworth. Longworth asks her to run a plate number for him.
At Hasker Recovery Yard, Longworth confronts Big Jack about lying to him, explaining that he knows Big Jack was drinking alone at the Rusty Crab till 2 a.m. when the owner called him a cab because he couldn't get a hold of Hal. Big Jack says Hal asked him to lie for him, to which Longworth adds "Because you think he killed your nephew." Big Jack counters that Hal could never do it because he doesn't have the balls, but Longworth says he's still taking Hal in for questioning.
In the interrogation room, Hal admits that he was present the night of Johnny's murder, but never even saw his cousin and was only there to find the coordinates. Longworth isn't buying it and argues that Hal was just waiting to push Johnny off his pedestal and that that night was perfect time. Hal argues that he just wanted to win back his family's good name, but when he got to Johnny's, the coordinates were gone and all he had was a bunch of artifacts that meant nothing. Longworth considers this.
Sanchez and Longworth study the artifacts from Johnny's boat in the lab. As they mull over the objects, Sanchez tells Longworth he's discovered that the swelling on Johnny's ankles was a vibrio infection which was caused by Johnny scratching his bites and then coming in contact with a nasty strain of vibrio vulnifus (a bacteria only found in brackish water).
Back at his house, Longworth and Callie pore over books looking for the location of this brackish water, where salt and fresh water mix. Longworth and Callie discuss the attack on the Magdalena. They note that the pirate Black Jack seemed to know exactly where the ship would be before the attack, meaning that maybe he had an inside man helping him. Longworth explains that knowing who this inside man was will help them figure out where Johnny was in his quest for the treasure. Callie shows Longworth something in one of the books, adding that maybe following Johnny's trail will help them find the killer. Longworth agrees that they need to look at the person who checked out these books last, and he thinks he knows who that person is.
Longworth stops by Ellison's to talk about Dulce Mendez, noting that both she and Ellison checked out the same book at the library in the last six weeks, giving him a hunch that they know each other. As they talk, Longworth plucks a blond dog hair off Ellison's robe, the same kind he discovered on Mendez's shoulder. He adds that he's also seen a car with consulate plates parked up the street. Ellison explains he checked out the book to learn about his investment and Longworth will have to talk to "that parasitic bitch" to find out what she was up to. Longworth says he's confused: if Ellison feels that way, why is he sleeping with Mendez. As if to prove his point, three FLDE agents grab Mendez as she attempts to dress and sneak out Ellison's back door.
At the station, Mendez tells Longworth that who she loved was nobody's business, but if the Spanish government found out she was having an affair with an investor for the Magdalena savage effort, it might be perceived as a conflict of interest. She continues that Johnny knew about the affair. In another room, Ellison adds that he told Johnny the affair was improving their negotiating position. Longworth asks Ellison where he got the bites on his arms and Ellison deflects that it's Florida and you can get them anywhere.
Back with Mendez, Longworth asks her how much she got for helping broker the deal for the Granada. Mendez tells him she got nothing and she did it for love of her country. Longworth says she's a better person then he as he only does his job for money. He continues that he thinks Mendez saw an opportunity to seduce Ellison into helping her find the debris field.
Longworth then explains his theory to Ellison: He and Mendez killed Johnny, stole the coordinates and were waiting until the murder case blew over to discover the treasure. Ellison argues that he would have no idea how to haul artifacts from the ocean floor and plus they could not profit from the artifacts anyway. Longworth counters that they could've melted the artifacts down for the gold and sold the rest on the black market with Mendez's connections.
Later, Manus tells Longworth Dulce Mendez is threatening to sue the department for malicious prosecution. In the meantime, Longworth says, he's trying to figure out what Johnny spent the hundred grand on. Manus tells Longworth Johnny spent it on marsh in some worthless swamp. But Longworth believes the swamp wasn't worthless, as Johnny was onto something that suggested the treasure from the Magdalena wasn't at the bottom of the ocean, but buried in the mangroves, which would explain how he got the bug bites. Longworth continues that Johnny must have had a general idea where the treasure was, possibly because of a map or some other instructions left by Black Jack.
Callie rushes over to Longworth's to tell him she's figured out there was no inside man in the Magdalena attack. Instead, it was an inside woman, none other than Magdalena herself. She shows him two portraits, one of Benito Francisco and Magdalena and the other of Black Jack and a young rogue, noting that both women are Magdalena and that the regal woman was in fact in love with the bad boy pirate. The two planned the attack together so they could run away, but were killed by her husband before they could. Unfortunately, Callie says, the portraits only prove that the two were in love, but not where the treasure is. Longworth disagrees, explaining that he thinks they do.That night, Longworth and Callie look for clues on the artifacts in the evidence room. Studying the portraits, Callie notes that in the etching of Black Jack and Magdalena, Magdalena holds his helmet in her hands. Longworth pulls out the pitted helmet from evidence and studies it, wondering why if she renounced her marriage and he wasn't Spanish, they would have an etching with a Spanish conquistador helmet like this one if it didn't mean something.
Longworth runs his finger along the top of the helmet inside and takes it out, black with soot. Realizing something, he grabs the evidence bag with the burnt candle in it, uses some matches he finds in his drawer to light the candle and sets the helmet on top. He explains that Johnny recovered the helmet from one of the many debris fields he salvaged trying to find the Magdalena and took it with him when he left the treasure hunting business, only this keepsake was actually the key to the Magadalena puzzle. When Johnny went broke, he figured finding the Magdalena could save him. Without enough money for a full expedition, he used the Internet and library research to come across a conclusion about where the treasure was. Longworth shows Callie the light from the candle poking through the pit holes in the helmet and explains that it represents the coordinates of the Magdalena on the night it was attacked: the exact conclusion Johnny was killed trying to prove.
Deep in the mangroves and far from all civilization, Longworth and Callie slough in the brackish water with a metal detector and a GPS, trying to follow the coordinates to the treasure. Despite the GPS, they are totally lost. Suddenly, just as Callie is ready to leave for the car, the metal detector starts beeping like crazy above a small, four-by-six foot object that seems just in the right spot. The two start digging.
Before long, Longworth's shovel hits on something hard. Longworth and Callie get on the ground and start shoveling dirt with their hands. Finally they pull a very old chest from the ground nestled next to two others. Longworth opens the chest. It's full of gold, silver and precious gems. Longworth and Callie debate what to do with the money, noting they could quit their jobs and do anything, but if they don't give it to the proper authorities, than they'll be the bad guys. But before they can make a decision, Ellison and Mendez sneak up behind them and put guns to their heads.Ellison makes Longworth and Callie get out of the hole with the treasure while Longworth explains who the two gunmen are. Ellison explains he didn't know where the treasure was till Longworth and Callie led him to it. As Ellison prepares to shoot them both, Longworth silently communicates a plan with Callie. They begin arguing with each other like a married couple, which dissolves into pushing and shoving until Ellison doesn't know what to do or who to shoot. While they're distracted with the staged fight, Longworth and Callie quickly grab Ellison and Mendez and wrestle their guns away from them.
The next day, the station conference room is buzzing with reporters and cameraman all jostling to see the Magdalena treasure laid out on the table. Manus tells the reporters that for now, the Magdalena treasure is evidence in a murder trial and after that it's up to the courts to decide, but in the meantime the FDLE will ensure that the treasure is kept safe.
As Manus continues to speak, Callie and Longworth talk about the previous night and their very close brush with death. Callie tells Longworth the experience has made her decide that life is too short to be chasing a fantasy and that she no longer wants to be with a man who let her down. Instead, she wants to be with someone who she can count on and loves her son and wants to be her friend. With that, she tells Longworth she is going to tell Ray she wants a divorce. Longworth says okay and Callie turns and goes, leaving the detective lost in thought.