One of Shawn and Gus's old camp buddies, Jason Cunningham, comes to them for help. He bought Camp Tikihama and is planning to reopen it, but one of his counselors has gone missing. Shawn, who was less friendly with Jason than Gus was, suggests he contact the authorities. But Jason explains that he's not positive anything has actually happened to her. Annie is mostly a loner who often goes off on her own. And involving the authorities would invite possibly unnecessary negative press that might kill the camp before it's even open.
On the way up to the camp, Shawn and Gus nearly run into a creepy old man on a bike who warns them they are doomed. Shawn wants to turn back but Gus convinces him to go on. Once there they meet the other counselors, Clive, Billy, and Sissy. Jason, who is now acting evasive and weird, asks Sissy to show them around. They go into the camp house, the last know location for Annie, and Shawn notices some broken glass by a window. As they tour the grounds, Gus reminisces about their camp days but Shawn mostly remembers how the camp was shut down when an electrician was electrocuted and died in the swimming pool. They hear a weird noise coming from the laundry shack, and when they go to investigate, Gus, trying to impress Sissy, opens the dryer to find Annie's bloody clothes and shoes.
Clive, Billy, and Jason arrive and, as Gus cleans his bloody hands off on his pants, Shawn tells them he suspects the old man on the bike. But Jason insists that "Crazy Old Erwin," the camp's janitor, wouldn't hurt a fly. Billy notices that the dryer cycle had just started. The killer must be close. They should split up and search the grounds. Shawn insists it makes more sense to stay put and call the cops but Billy, Clive, Sissy, and Gus leave anyway. Billy ends up falling into a trap in the woods where an unseen man with a machete has been waiting for his prey. Juliet arrives and find Shawn hiding in a closet in the laundry room. Everyone left alive reconvenes in the camp house and Jason soon arrives, furious that Shawn broke his word by calling the cops and storms out in a huff. Shawn goes after him and finds Annie dead in the laundry shack. Just then, a hooded man with a machete bursts in. Shawn takes off running, but as he does so, he mentally reviews all the clues he's found over the past day and realization hits. He confronts the hooded man, whom he now knows is Jason, and claims everything that has happened has been staged. Impressed that Shawn figured it out, Jason removes his hood as Annie and Billy arrive. Jason explains that he is reopening the camp as a Murder Camp, where adults come to participate in a murder mystery, and he needed a great detective for a dry run. The counselors knew the truth about the camp but were caught off guard when Jason started the game without telling them. Jason asks Shawn how he figured it out and he says the biggest clue was when Gus, who hates the sight of blood, wiped Annie's on his pants, knowing it was fake. Gus was in on it with Jason, getting Shawn back for a lifetime of pranks. As it starts to rain, Jason gets everyone inside for celebratory champagne but the party is short lived after they spot Erwin floating dead in the lake.
Juliet tries to call for help, but the storm has knocked out all communications. She tells everyone not to go near the body until forensics can get there, even though there are no signs of foul play on the body. Billy suggests a game of strip cribbage while they wait, but Clive, sensitive about his body, opts for video games and Annie leaves to take a shower and wash all the fake death make-up off. After Shawn expresses some suspicions to Juliet, she lets him take a quick look at the body where he sees a mark on the side of Erwin's neck. Annie, meanwhile, gets out of the shower to discover a hooded man with an axe waiting for her. At first she thinks it's Jason, but is surprised to find she's dead wrong. Back at the camp house, the lights go out. Billy leaves to check the breaker, but the hooded man surprises him, electrocuting him in the fuse box. As the lights come back on, Shawn realizes that Clive's ring matches the mark on Erwin's neck but when he goes to confront him, he sees that Clive hasn't been playing video games for some time. Clive is the real killer. When he returns to finish the rest of them off, he explains that his father was the electrician that was killed there years ago, and he was filled with murderous rage when he found out that Jason was planning on making a game out of the tragedy. Juliet shoots Clive in the hand, sending his machete flying before he is able to kill anyone else. As the storm breaks and the sun rises, help finally arrives but Tikihama will never be the same again.
Meanwhile, Lassiter is invited to dinner by Victoria Parker . Thinking it's a date, he buys her a necklace, and is surprised when she erects divorce papers.
- A pineapple appears in the form of a pinata in the flashback. There is also one in Annie's fridge.
- The title is a nod to the Friday the 13th series of slasher films, and the frequent occurrence of paraskevidekatriaphobia. The original airdate of the episode was also on Friday, February 13, 2009.
- The song that plays when you see Shawn's piñata is the same song Dwayne Tancana sang in "Bounty Hunters!".
- The doll that Jason carries looks very similar to "Robert the Doll", a famous haunted doll.
- Annie's fridge is the same as the fridge in "Shawn (and Gus) of the Dead".
The gallery for Tuesday the 17th can be found here.