The whole SBPD crew is at a local bar celebrating the retirement of a fellow officer. Shawn makes a toast to Jim Dubois, the retiree, then calls for a round of shots. Juliet heads out early, leaving Shawn and the boys alone for a night out drinking.
Cut to the next morning at the Psych Office. We see Shawn and Gus passed out. They finally awake and have absolutely no idea what happened the night before. They are clueless as to why Shawn is wearing a shower cap, a gold chain and sandals that are not his, why Lassiter is there with a black eye and why Woody is also there both not remembering anything about the night before! There is strange debris everywhere, seemingly all clues to what happened last night.
Shawn tries to recall visions from last night, but every image is distorted. They search the room for clues and discover Lassiter's gun is missing three bullets, his car keys are missing, there is a huge dent in the blueberry, and there is cell phone video footage from the night before. They watch the video and see they were very chummy with a Hawaiian Shirted Man.
Just then, Woody gets a call from his office. They all head to the morgue where they are mortified to discover that the same Hawaiian Shirted Man is now dead on the slab, shot exactly 3 times &ndash which immediately leads us to believe that Lassiter's gun could have been the murder weapon. Shawn then realizes that the sandals he is wearing belong to the dead guy. Then, they realize that Gus and the dead guy had accidentally swapped phones and that they had his phone the whole time.
Concerned, Juliet pulls Shawn aside and asks him about the "strange, game-changing" phone call he made to her last night. Shawn doesn't remember it one bit, and Juliet needs to leave before she can get into any details.
Lassiter, Shawn, Gus and Woody all determine that they must have been drugged, as they remember none of this. Woody gives a drug test to all of them and confirms it... but who drugged them and why? The guys find more clues on the dead guy's phone: numerous pictures of a woman. Since they remember absolutely nothing from the night before, they head back to the bar they were at to get some answers.
Shawn theorizes that they may have been the unintended recipients of a round of drugged drinks from a guy sitting at the bar. But the bartender squelches that theory the second he reveals that the man Shawn thinks drugged them, is his partner, as in, his lover.
Just then, a super hot woman enters the bar, walks over to Gus and kisses him. Gus thinks this is some girl he hooked up with from the night before. The Hot Woman tries to get Gus to go with her, but Gus reluctantly stays to finish the investigation. Just as the hot woman is giving Gus her number, Shawn remembers a few clues from the Psych Office that lead him to believe they went to Bobo's Donuts after they left the bar.
They arrive at Bobo's Donuts and discover they had been there last night questioning the Shop owner about the woman in the photos. It turns out their Hawaiian Shirted friend was hired to find the woman in the pictures because she was suspected of cheating. They take a look at the security camera footage from Bobo's: a Man punches Lassiter in the face, and the dispelled bullets from Lassiter's gun were used to shoot at the giant Bobo's Donuts statue that fell on the Blueberry, causing it to be crushed.
Just then, Lassiter gets a call: another dead body. The body belongs to the same man who punched Lassiter in the security footage! Shawn figures it out that Scott and the Hawaiian Shirted P.I. knew each other and were in contact because the P.I. had Williams' number in his "recently dialed" call history.
Our guys and the SBPD are now at Williams' home investigating the murder. Shawn realizes from a photo in the house that the pictures of the woman the P.I. had on his phone are of the same woman who lives there. In fact, she is Scott's wife. They then determine that the P.I. was hired by Scott to investigate his cheating wife. Now, they think it was the wife that killed both of them.
Just then, Shawn gets a worried call from Henry who is at a motel room and has no idea how he got there and why. From this, Shawn puts it together that they must have went to this same motel last night thinking the wife was going to show up there. They get confirmation of this by checking out her vacated room. But the room is rigged to blow up via gas leak, so the guys quickly escape by jumping off the balcony and into the unkempt pool.
Back at the SBPD, while Vick is lecturing everyone about their recent behavior, the real Ed Lover shows up to retrieve his gold chain that Shawn apparently stole off of him at a club the night before. Just then, Gus gets a call from the hot woman. Having had enough of all this, he leaves to meet up with the hot woman.
Next, they all analyze the photos from the P.I.'s phone. Shawn takes a closer look at a picture and recognizes the face of a man the wife is eating lunch with. From there, Shawn gets SBPD's tech guy to alter the face in the picture to look like the mug shot of a man on the Most Wanted List - a man named Leroy Jenkins, who looks just like the man the wife is eating lunch with in the picture. After a few adjustments to the photo, Shawn's theory is proven right. Leroy had been keeping a low profile for years, and when he found out he was being followed by a P.I., he had both Scott and the P.I. killed. Then they all realize that Leroy wasn't working alone, and that his partner was Leroy's next of kin, Lilly Jenkins. She is the same girl who approached Gus and kissed him at the bar. She was actually at the bar that night tracking the P.I. to get his phone to wipe any evidence he may have recorded of her dad Leroy Jenkins. But when she saw there were cops, she drugged them to make sure they wouldn't remember any of the events surrounding Leroy's whereabouts. And Shawn puts it together quickly that Lilly is the same Hot Chick that was all over Gus, and that she was only after Gus to get the P.I.'s phone, which is also the same phone Gus still has in his possession.
SBPD immediately heads over to Gus's apartment to save him from being killed by Lilly. When they arrive, Lilly has already drugged Gus, and Leroy is there with a gun pointed on a woozy Gus. Lassiter and Juliet show up just in time, take down Leroy and arrest him once and for all.
We end with Shawn and Juliet discussing the fact that Shawn, in his drugged state from the night before, called Juliet suggesting they move in together. Surprisingly, in the end, Shawn is the one who suggests that they actually do move in together. However, Shawn is shocked when Juliet tells him she isn't quite ready to make that next step.