Vick wants Lassiter to take a case that he really doesn't want to. He looks up and sees Shawn and Gus putting on a psychic show for the other officers and gets an idea. He calls them over and says he's got a case for them. He hands Shawn the case file and tells him the victim is waiting to give a statement. As they walk into the interrogation room, they find a fully unclothed man, Fred Turk. With Lassiter happily watching through the one-way glass, Shawn and Gus proceed to give a very uncomfortable interview in which Turk claims he was abducted by aliens. As Turk tells them he woke up naked in a field with a headache, Shawn spots a faded ink mark on the guy's hand and chafe marks on the back of his heels.
The cops think Turk is a nutcase but Shawn knows the guy was dragged into that field. There was a crime committed here, he's just not sure what. Turk wasn't assaulted or robbed, but he was probably drugged with a hallucinogen. He also said he remembered a strong lavender scent and seeing barbed wire. Shawn knows exactly where that is.
When they get to the field, the police are already there - with another naked guy, Phillip Keiser. Shawn notices a tire pattern in the dirt, a broken strap off a woman's shoe and a spider web broken at a low level as if someone short had walked through it. Keiser says he doesn't remember anything and woke up with a headache, same as Turk. Shawn sees another partial ink mark on Keiser's hand and notices he has no tan lines anywhere on his body, same as Turk, which leads them to their next stop, the only tanning salon near where both the victims live that has the new "Insta-Tan" process, the only process capable of producing their flawless liquid tans. The attendant at the salon tells them that both Turk and Keiser were regulars and that it's always the single guys who keep up their tans. Shawn remembers the shoe strap and figures a woman might be targeting single guys at the salon, that is, until they run into Henry who tells them as an ex-cop and a regular at the salon, they are looking in the wrong place. Just then Shawn gets a call. There's been another victim, but this time he's dead.
Back in the field, Shawn spots a green smudge on a fence post. He also sees that the victim is pale - so much for the tanning salon theory. One thing the latest victim does have in common with Turk and Keiser is the partial ink stamp on his hand, all three of which, pieced together, form a four-leaf clover, giving Shawn his next lead. They head to Shenanigans Irish themed eatery, complete with green popcorn, and talk to Marvin, the host. Shawn sees the stamp, which matches the marks on all the victims' hands, and Marvin tells them it's only used for their events, like speed dating.
They go and talk to Turk, who confirms he participated at the speed-dating event. He also tells them strange things have been happening to him ever since. He was the perfect candidate for a job he applied for but was rejected at the last minute. The company told him they received a call about him but said it was confidential. Shawn is even more convinced the key lies in the speed dating and talks Vick into ponying up the entrance fee after he tells her he's looking for a short woman with a particular tire on her car, and draws them the pattern he saw in the field. Lassiter tells them that the dead victim had the same non-lethal dose of drugs in his system of Turk and Keiser, but he had a pre-existing heart condition that made the dose fatal and the murder accidental. He thinks they should just haul the women into the station and question them all there but Vick says that would tip their hand. They all must go undercover at the speed-dating event.
Back at Shenanigans, Lassiter tells Shawn he ran the tire pattern and they are looking for a woman with a late model American sports car. Just then Lorraine, the woman who runs the event, tells them the rules and gives them personality questionnaires to help match people up. During the speed-dating, Shawn talks to a woman named Glenda, who asks him about his mother's maiden name, his pet's name and his favorite color, but later on meets a girl named Darcy, who not only fits all their suspect requirements, but also works in pharmaceutical sales, giving her access to drugs. Her questionnaire also matched perfectly with Gus', so they set up a date to get more information. On the date, Gus tells her he lives at the beach, so when she says she wants to go back to his place, they are forced to go to Henry's, who tells them that she's not the one they are looking for. She's too sincere.
Lassiter calls Shawn to the police station where they are holding Marvin. They found him outside one of the speed-daters apartments and they discovered a stack of stolen questionnaires at his house. Shawn notices a green smudge on them similar to the one he saw on the post in the field. He knows Marvin had something to do with it and suggests they follow him to work and he'll lead them to his female partner.
At Shenanigans, the speed dating is already in progress and Shawn overhears Glenda asking another guy the same questions she asked him. She's also exchanging glances with Marvin and has a similar tan line on her ring finger as him. With that, he's figured out that they are not only partners, but also married. And they used the speed dating as a cover to get credit card and personal information to steal people's identities and then drugged and dumped them into the field to cover their tracks.