Three actors from Clue made guest appearances in Psych's 100th episode, which served as a tribute to the 1985 comedy. The USA series, known for paying homage to various genres, movies, and TV shows throughout its eight season run, occasionally devoted entire episodes to a specific film or show. When Psych paid tribute to Twin Peaks in season 5, it brought back a long list of actors from the show.
Psych repeated this formula in season 7 for its 100th episode, appropriately titled "100 Clues". The episode sent Shawn (James Roday) and Gus (Dulé Hill) to a mansion owned by a member of a rock band. Following Shawn and Gus' arrival, they met a colorful assortment of characters. Before long, a dead body was found. To make matters worse, they were unable to leave the house, as a panther was wandering around outside. They were soon joined by Juliet (Maggie Lawson) and Lassiter (Timothy Omundson), who helped Shawn and Gus get to the bottom of the mystery.
The characters and setup for the plot in "100 Clues" made it clear that the episode was Psych's take on "Clue", the popular mystery board game where players have to identify the scene of the crime, the killer, and the murder weapon. It even included the character archetypes from the game. But it was actually more of a tribute to the 1985 film adaptation of the game. Many of the scenes that took place in the episode were references to events that took place in the movie. Like the movie, "100 Clues" featured alternate endings where different characters were revealed to be the killer. Also, three of the guests - or suspects - in "100 Clues" were played by actors from the movie.
- Christopher Lloyd as Martin Kahn: Christopher Lloyd played Professor Plum in Clue. In "100 Clues", Lloyd was Martin Khan, the band's biographer. In one scene, Martin says Lloyd's famous Back to the Future line, "Great Scott!" In one of the alternate endings, Martin is revealed to be the murderer. This was also the case for his Professor Plum character in Clue.
- Martin Mull as Highway Harry: In Clue, Martin Mull played the role of Colonel Mustard. The actor portrayed an entirely different character in "100 Clues". Mull's Highway Harry was the band's manager and an alcoholic who was drunk for most of the episode. He was originally believed to be one of the murder victims, but it was discovered later that he had only passed out.
- Lesley Ann Warren as Leslie. Lesley Ann Warren, who portrayed Ms. Scarlett in Clue, played a groupie. It was explained in the episode that her character had a history of trysts with people associated with the band, including the real murderer, Clizby (Garrett Morris).
"100 Clues" wasn't able to bring back any other major cast members, but it's worth noting that Tim Curry (who played Clue's protagonist, Wadsworth) already had a role in Psych. In the season 1 episode, "American Duos", Curry played Nigel St. Nigel, who was a parody of American Idol judge Simon Cowell. In the credits of "100 Clues", it was stated that the episode was dedicated to Clue star and Mrs. White actress Madeline Kahn, who passed away in 1999.