Prince Viktor pours a drink for himself and a wary Adalind. He's devastated by his cousin Eric's untimely murder - therefore, Viktor's retaining Adalind's legal services. In order to gain his trust, he charges her with composing a list of potential Portland murder suspects. What she doesn't know is Viktor has installed hidden cameras in her hotel room, observing her rub blood on her pregnant belly.
A hulking man rummages through a nice house, stuffing expensive items into a rucksack. Suddenly, Scott, a young man fresh off a plane from college, opens the door. The house is a disaster zone and a quick minute of investigation reveals the massive intruder. Though he attempts to defend himself with a kitchen knife, it's no match for the robber, Gregorek, who promptly morphs into his reptilian Wesen form.
Nick and Hank's investigation is gruesome - Scott's arm was pulled out of the socket and blood spurted to the ceiling. Bloody footprints indicate the murderer's shoes are size 15 or larger. Some research back at the precinct tips off Nick that there might be a trend - this is the third robbery in that neighborhood. Harper's autopsy shows Scott died from a broken neck, but his extensive injuries include multiple fractures and bite marks. The only similar injuries she's ever seen were from a shark attack...
Renard's new location is known only by him, Meisner and the castle spy. After he spends several days waiting in a safe house, the family calls on Renard. Upon their arrival, Renard and Meisner are led to the "trial" of the man who set them up and they watch as the torturer, Frenay, repeatedly asks for a woman's name. When the accused finally whispers it in Frenay's ear, he's promptly shot.
Across town, a storm drain maintenance team lowers a worker, Jimmy, into a manhole. Alone in the storm drain, Jimmy calls out that he doesn't see the source of the blockage. Venturing further in, Jimmy discovers a tree blocking the sewage, but Jimmy is thrown off by the sound of footsteps deeper in the tunnels. There's not another crew working on the blockage... Up above, the rope goes taut while Jimmy's screams echo through the tunnels. His crewmates quickly pull Jimmy's limp, bloodied body out of the manhole.
Jimmy's five minutes in the storm drain proved fatal. The only similar injuries the paramedics have ever seen belonged to a bear attack. Wu is positive it's an alligator's bite marks. A freaked out Wu, along with Nick and Hank, follows the supervisor into the drains. Near the blockage, several personal items float in the water, along with Jimmy's missing leg.At the precinct, the police officers identify the odd assortment of items pulled from the drains: all of the possessions belonged to people whose homes had recently been robbed, including Scott, the murder victim. The coroner's report reveals that the bites do resemble an alligator's teeth - but alligators don't rob houses.
Of course, Monroe's heard the legends of alligator-type Wesen called Gelumcaedus. Nick and Hank bring Aunt Marie's book for a group story time session and Rosalee reads aloud that Gelumcaedus are one of the oldest known Wesen, dating back to the fall of Rome. Grimms use a special weapon against this Wesen called a vambrace, a metal forearm sleeve with a wicked-looking hidden blade. Nick is sure he's seen the instrument in the trailer. Strapping on the weapon, Nick flashes back to killing the man in the bar...
Since Gelumcaedus have lived in underground tunnels since ancient times, it's a safe bet the rogue Wesen is hiding in Portland's 400 miles of storm drains. A city worker informs the Grimm the only drain entrances are manholes and outfalls. Pouring over a drain map, Nick and Hank pinpoint outfalls near three looted neighborhoods. The Gelumcaedus must use the outfalls as escape routes and live in the center where the maintenance worker was murdered.
Armed with night vision goggles and Nick's vambrace, the detectives search the tunnels for signs of life. Nick finds a door hidden behind moss revealing the Gelumcaedus' loot, loot that must have come from multiple cities. Perhaps he's killed people in other cities. Suddenly the hulking mass jumps Nick and Hank! He's no match for a Grimm though and he's dragged down to the police station for questioning.
The Gelumcaedus' name is Gregorek and he has a record: arrested in Salt Lake City and NYC for breaking and entering, but acquitted for lack of evidence. Monroe answers Nick's burning question: when he arrested the Gelumcaedus, Gregorek called him "decapitare," old-school Latin for "he who decapitates." At the station, Nick discovers that, based on the robberies' timetables, Gregorek had a partner...