"Thrill Seekers and Hell Raisers" is the eleventh episode of season four. When Shawn and Gus join Gus' new girlfriend on a rafting trip, a member of the group is lost overboard, but Shawn quickly realizes it was no accident.
Gus has a secret girlfriend that he has been keeping from Shawn, but now he is finally ready to introduce him to Ruby. Shawn's first impression of her is a good one, as she is a caring person and matches him in several pointless trivia tests', but he insists on meeting her friends to vet her further. So he forces Gus to crash what he thinks is a picnic with Ruby and her friends Jessica Martino, Derek, and Stu Crawford. The guys, however, soon learn they have walked into a river-rafting trip instead. Ruby is thrown at first, saying there is not enough room, but then relents and hooks them up with gear. Shawn thinks Ruby might be hiding something, and uses his 'psychic' abilities to break the ice with her friends by 'divining' Stu is the most experienced of the group. He doesn't need his skills with Jessica, who makes a move on him. Gus uses a more direct approach and asks how they all met. Ruby says Derek and Stu met at a Wildlife Preservation meeting, which is ironic because Derek was a big game hunter back when he dated Jessica, who is Ruby's work colleague. What binds them all together is their interest in extreme sports. The group then hook whistles to their vests in case they get separated. Shawn and Gus realize they are on a white water trip just before they hit the rapids, and they hold on for dear life. When they come out the other side, they realize Stu is missing.
Rescue workers are called out to search the water for Stu, as Lassiter and Juliet take statements from the group. Shawn thinks Gus should stay far away from Ruby and her attraction to dangerous activities, but Gus isn't ready to let her go. The rescue team finds Stu's life jacket and Lassiter suspects it came off when Stu went overboard. He most likely hit his head and drowned. Shawn remembers that when Stu was attaching his strobe, he had an extra hook on his jacket. He now sees that both hooks are gone. Shawn tells the group that Stu didn't drown, he swam away. Back at the police station, Shawn says Stu must have hooked himself to something in the river. The cops tell him they found netting rigged under the water. Stu knew exactly when to jump out of the boat and used the equipment to hide until the raft was out of sight, then he headed for shore. Juliet tells them that Stu and his business partner, Brian Sampson, just filed for bankruptcy. Lassiter says they need to talk to Sampson, because it's unlikely Stu pulled this off himself. Shawn then remembers Ruby made him switch seats with Stu when they were getting in the boat. Shawn pulls Gus aside and tells him his suspicions, suggesting they use Ruby to find Stu, but Gus doesn't believe him. So Shawn has Gus and Ruby over to Henry's for dinner so Henry can back him up, but Henry isn't so sure. Ruby tells Gus she thinks Shawn doesn't trust her. Gus then informs her of Shawn's suspicions and she confesses. Stu is one of her best friends and he needed her help. The company was filing for Chapter 11 because of Brian's exorbitant lifestyle, and the way he used company money to finance his extravagance. She swears Gus to secrecy, making him promise specifically not to tell Shawn.
Back at the police station, Juliet tells Shawn they were unable to find Sampson, but they brought his assistant, Charles Lucas into custody. As Shawn and Gus go to see if they can glean anything from him psychically, Shawn realizes Gus is avoiding him. Shawn remembers seeing Lucas at the river, but the assistant claims he was just there to drop off Stu's car. Shawn doesn't see any signs of lying from Lucas, but notices Gus is exhibiting all of them. Shawn accuses Gus of hiding something, but he denies it. Juliet then tells them they found Sampson's body in the woods, the victim of an apparent hunting accident. She also says Stu and Sampson had million dollar life insurance policies on each other, which gives Stu a motive for killing Sampson. Shawn tracks down Ruby and her friends at a rock climbing wall to find out what Gus is hiding, but he covers with her friends, telling Derek he's there chasing after Jessica, who still shows signs of being interested in the psychic. Derek wishes him luck and offers to give him his key to her apartment. Gus is there, too, and tells Ruby he thinks it's time to tell Shawn everything, given Sampson's death. She's shocked to learn of the murder, and claims Stu is innocent, even though it was Sampson who was bankrupting the company. But Ruby comes clean and Shawn is able to psychically lead the police to Stu's hide-out, only when they arrive, they find Stu dead of an apparently self-inflicted gun shot wound.
Chief Vick, along with Shawn and Gus, questions Derek, Jessica and Ruby but none of them know anything else. On the way out, Shawn gets a glimpse of a picture Stu's body on an autopsy report, then visits the coroner who tells him Stu was shot with a Winchester 70 rifle. Shawn psychically reveals this information to Lassiter and Juliet who tell him Jessica owns that same gun. Shawn calls Gus to warn him and Ruby away from Jessica, but Gus tells him Ruby is safely paragliding with Derek. Meanwhile, as they are getting ready to take off from the cliff, Ruby gets a look at Derek's GPS and sees he was at Stu's hide-out. Derek is the killer.
Back at the Psych office, Shawn remembers that Derek was a hunter and has a key to Jessica's apartment. He and Gus rush off to save Ruby, who is stalling for time with Derek. Derek tells her he made a pact to help Stu with Sampson, to make him pay for what he did to Stu. But when Stu found out that he murdered Sampson, he freaked out, so Derek had to kill him, too. Shawn and Gus arrive, and Gus lunges for Derek, knocking them both into a glide off the cliff. Shawn, Ruby and the cops follow the glider as it comes back down to earth, where Gus is saved and Derek is arrested. Shawn spins a tale of Gus' bravery and fighting prowess, which they agree is the way the story will be told from here on. Sadly, Ruby unilaterally decides that the attraction may have been rooted in adrenalin, and she and Gus need a cooling-off period, to see if the pull is real. Reality returns as the duo discuss the idea of the movie 'Alive' and how long Shawn should wait before eating Gus. Juliet and Lassiter are sucked in, and it turns out Lassiter has given the matter, and related concepts, more thought even than Shawn.
As Lassiter was telling Ruby and her friends what he believed happened to Stu, Jessica can be seen smiling in the reaction shot, trying not to laugh. Ironically, in the next cut back to her, she walks away crying.