Steve Franks, creator of the series, returned for the fourth season as showrunner. The theme song, "I Know, You Know" by The Friendly Indians, continued to be used, though it was edited twice: in "Bollywood Homicide", the song was given a Bollywood theme with the lyrics sung in Hindi, while Boyz II Men performed an a cappella version for "High Top Fade Out".
Steve Franks wrote five episodes, while Andy Berman wrote four and Kell Cahoon, Saladin K. Patterson and James Roday wrote three. Returning for two episodes each were writers Tim Meltreger and Anupam Nigam. Bill Callahan and Todd Harthan joined the writing team, with Callahan writing three episodes, and Harthan writing one.
While on vacation in Vancouver, Shawn and Gus are suddenly on the trail of elusive art thief Pierre Despereaux (Cary Elwes). Since Lassiter has been trying to arrest this criminal for years, he and Juliet arrive in Canada as well, and Shawn believes that this thief has pulled off the perfect crime, until he realizes what's really going on.
The private jet of billionaire hedge fund manager Warren Clayton crashes in a forest. Shawn and Gus manage to find him first and are asked to fulfill his dying wish: to find out who killed him. His widow (Christine Baranski) is one of the suspects, and as Shawn digs deeper, he uncovers more than a murder. At the same time, Abigail (Rachael Leigh Cook) insists on meeting Henry, which Shawn isn't ready for due to their complicated relationship.
An Old West tourist attraction called Old Sonora, run by Sheriff Hank Mendel (James Brolin), is in danger of being shut down due to sabotage. Since Lassiter is fond of the town - he spent many weekends there as a child - he enlists Shawn and Gus to investigate.
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4
"The Devil's in the Details... and the Upstairs Bedroom"
A college girl commits suicide at a Catholic University. While Shawn believes it to be mere suicide, Father Westley (Ray Wise) - one of the professors at the school - and Gus are convinced the girl was demon-possessed. Although he is skeptical towards that idea, Shawn decides to play along, until the case takes a turn.
As Shawn, Gus, Lassiter, and Juliet are celebrating Buzz McNab's birthday in a police bar, somebody attempts to rob the place and engages in a gunfight with Lassiter. It is believed that the incident was a random attempt at robbery until Shawn reveals that the gunman (Stephen Lang) was targeting a cop.
A young East Indian man named Raj (Sendhil Ramamurthy) believes he is cursed when all of his serious girlfriends have met with suspicious accidents. Shawn and Gus decide to figure out what the real problem is, and Juliet also gets involved in a big way. For Shawn, solving the case is a chance to get back at Lassiter for embarrassing him in front of Abigail (Rachael Leigh Cook).
The death of Leonard "Diddle" Callahan, a computer cryptologist who was the baritone in Gus’s old college a cappella group, is suspected of being murdered, by the other two members (Jaleel White and Kenan Thompson). Although they both had a falling out with Gus, they ask Shawn to investigate, but he and Gus find themselves stonewalled at every turn by the police, and later, an undercover detective (Tony Todd).
A man named Stewart Gimbley (Joshua Malina) believes he is a werewolf, so he offers Shawn and Gus three times their normal rate to tie him up and observe him. Unfortunately, they fall asleep and wake up to find Stewart missing, their window broken, and a tuft of animal hair. Their investigation leads them to a psychiatrist (David Naughton) and a Wiccan (Larisa Oleynik), each with possible secrets. This is also the episode where Henry has to keep touching a truck to win it.
Gus, O'Hara, and Lassiter arrive at a vehicle storage yard after receiving a message from Shawn. They realize he has been shot and abducted, so Henry works with Lassiter to find him, while Gus tries to remember the details of the case. Shawn realizes that his abduction is part of something much bigger after speaking with his kidnappers (Michael Rooker and John Hawkes).
Shawn deduces that a U.S. Army Private who was found hanged was the victim of foul play, and Juliet calls in her brother Ewan (John Cena), a former soldier who has DODSecurity Clearance to help them get on the Army base. Unfortunately, Shawn comes into conflict with Juliet over his hunch that Ewan is somehow more deeply involved with the murder. As the case proceeds, Abigail (Rachael Leigh Cook) has some unwelcome news for Shawn.
Gus reveals his new girlfriend Ruby (Sarah Shahi) to Shawn, who hasn't forgotten Gus' poor track record with women - while drunk, he married a crazy woman in 1997 - but immediately takes a liking to Ruby. Shawn and Gus join Ruby and her friends (Stacy Keibler and Steve Howey) on a river-rafting trip, and when one of them goes missing, Shawn figures out two things: it was no accident, and Ruby was somehow involved. Gus learns the truth, and is soon put in a compromising position.
In 2003, Juliet made a pact with her boyfriend Scott Seaver (Josh Braaten) to meet up in seven years. After he fails to show up, Shawn finds him, and by extension endangers his life since he was a key witness against mobster J.T. Waring (Arnold Vosloo), who was convicted for the murder of a U.S. Marshal. When Waring denies killing the Marshal, Shawn must prove him right in order to protect Scott.
A courier named Donny Lieberman (Ernie Grunwald) loses a cooler containing the deadly Thornburg virus, so he asks Shawn and Gus to help him find it, and Shawn realizes that the same lab that Donny was working for is somehow involved. Luckily, they get help from Dr. Steven Reidman (Judd Nelson), the foremost expert on the virus who also expresses interest towards Santa Barbara's favorite psychic. In the race to stop an outbreak, Shawn has an epiphany concerning Juliet.
Shawn and Gus are recruited by Walter Snowden (Bruce Davison) into a think tank, joining Boyd (Miguel Ferrer), Svetlana (Sandra Hess) and Alan (Alex Zahara) to help prevent the murder of business tycoon Ashton Bonaventure (Chris Sarandon). While Shawn doesn't shine in the group, he figures out that someone in the think tank was using it to figure out ways to kill Bonaventure, so he convinces Bonaventure to put him in charge of security and re-assembles the remaining members to help him prevent the assassination attempt.
A shark attack victim washes up onshore, and Lassiter notices what appears to be a knife wound on the body. With that, he thinks that the victim was actually murdered, which impresses Shawn since it is a theory that he would come up with. Meanwhile, Henry begins flirting with a shark expert (Jeri Ryan) and a fisherman (Michael Hogan) lends Shawn and Gus a hand.
As Mr. Yang's (Ally Sheedy) book is released, Shawn and Gus meet up with Mary Lightly (Jimmi Simpson), who believes that Yang had a partner (Christopher Turner), and he turns out to be right when a dead body (Beverley Turner) turns up. As another murder is committed, Shawn, Gus, Juliet, Lassiter, and Henry find themselves in scenarios from classic Hitchcock films in order to stop Yin. Just like Yang, Mr. Yin makes it personal when Abigail (Rachael Leigh Cook) is dragged into his game. However, she is not the only victim...
