Juliet surprises Shawn with tickets to Scare Fest, an event at the local theme park that hasn't taken pace in 15 years. But Shawn already had tickets to go with Gus. Not wanting to let either one down, Shawn decides to go with both on separate nights, but doesn't tell either one. Shawn already has enough tension built up with having to tell Gus about his and Juliet's relationship. He doesn't want either relationship to suffer because his attention is now divided.
On opening night, Shawn and Gus head into Scare Fest. They are instantly transported to back to their youth. But things turn sour when on the Haunted House ride, Shawn witnesses a murder. Shawn tells Carol, the ride operator, immediately after, but she doesn't believe him one bit.
Shawn and Gus discover their old assistant Ken is now working at Scare Fest. They convince Ken to help them break into the haunted house ride to get a better look at the possible murder victim. While inside the ride, Shawn takes Gus to the place he saw the man get murdered, but the man is nowhere to be found. After getting caught snooping around, the boys are brought into the fest's administration offices. There, they meet Eve, one of the park officials. The Park President's picture hangs on the wall and Shawn recognizes him immediately as the person who was murdered in the haunted house.
Back in the haunted house, the police are there checking out the body. But Shawn sees something fishy about the crime scene. Shawn saw the man get killed on the complete opposite side of the ride, and he wasn't wearing a mask like this dead body is. Mr. Holloway, the park's Vice President, steps forward and claims that he thinks the murderer was Johnny Rickets - or rather, the ghost of Johnny Ricketts. Holloway explains that Johnny Rickets was a kid that fell off the ferris wheel at Scare Fest 15 years ago and died. That was the last year they did Scare Fest - until this year, when they decided to open it back up. Holloway goes on to explain that he has been seeing Johnny Rickets everywhere, and that he thinks Ricketts is trying to tell him something beyond the grave.
Back at SBPD, Juliet tells the guys about some research she did on Ricketts's death. She discovers that Holloway was running the ride that night when Ricketts fell to his death. Back at the fest, the guys go looking for Holloway, but it turns out Holloway has been murdered on the log ride. The guys check the ride's photo-cam, and they are shocked to see Johnny Ricketts riding in one of the logs.
At this point, the park has been shut down, and SBPD is now on the hunt for the murderer at the fest. Shawn and Gus run into Ken and ask him about Johnny Ricketts and if he thinks Holloway's and Wayland's deaths are linked. Ken tells them that they should look in the archives, as the park keeps everything on record. While there, Shawn discovers that Eve was also there the night Ricketts died, and that Holloway and Wayland made Eve falsify statements about the death of Johnny Ricketts. Then Shawn discovers that the park paid the Ricketts family off for his death. But then they see that another person was paid off by the park - a Jamie Emerson. Suddenly Eve shows up. Shawn tells Eve he knows about the payouts and the falsified statements. He questions her, but Eve gets scared and runs away.
Back at SBPD, they discover that there is no death certificate for Jamie Emerson. Jamie only has a California I.D. because she can't drive due to an injury. This is where Shawn discovers that Jamie was there with Ricketts on the ferris wheel the night he died, and that she is the one who is murdering everyone who lied about Ricketts's death. They immediately go looking for Eve because she is next to be killed. They find Eve and she admits that she has also seen the ghost of Johnny Ricketts. Then suddenly, the ride operator Carol shows up. Shawn immediately knows that she's the murderer and that her real name is Jamie Emerson. Then Shawn puts the rest together: Johnny was trying to save Jamie's life on the ferris wheel because her latch belt wasn't properly locked. But it was Johnny who fell and Jamie who survived. The park never came clean about the accident publicly, and Jamie had to live with knowing Ricketts's death was a cover-up for the last fifteen years. But Jamie wasn't working alone - there was no way she could have ran the ride and killed Wayland at the same time. She had a helper. Shawn flashbacks to the moment he saw the ride operator, Carol (Jamie), texting with Todd, the fest's guess-your-weight-guy. This leads him to believe that Todd was in on it. Shawn figures it out that Jamie and Todd dressed as Johnny Ricketts when they murdered Holloway and Wayland. Then suddenly, SBPD arrives and saves Shawn, Gus, and Eve from nearly getting killed by Todd and Jamie.
In the end, Shawn finally tells Gus about him and Juliet dating. And much to Shawn's surprise, Gus isn't surprised at all to hear this news.
The title is something of a portmanteau concept, blending 'in plain sight', in the sense of 'clearly visible', with notions of fear.