Lucy Ryan is the main villainess from "The Devil's in the Details...and the Upstairs Bedroom," episode 4.04 of Psych.
She was played by Alexandra Krosney.
Lucy Ryan is a student at a Catholic college and the best friend of fellow student Agatha Brontus, who jumped off the roof to her death right in front of her. It was later revealed that Lucy had caused Agatha's death, as she had been wanting Agatha's boyfriend, Cameron, to herself.
During confession, Lucy revealed to Father Westley that she had feelings for Cameron, and she set out on a plan to break them up. She stole Westley's medication for Parkinson's Disease and drugged Agatha, hoping to make her crazy and that Cameron would break up with her. The couple did split, but it was Agatha who dumped Cameron, fulfilling Lucy's evil plan. However, the medication was making Agatha immensely unstable, and it led to Agatha jumping to her death as Lucy chased her.
Lucy was present as the SBPD, Shawn, and Gus were at the scene of Agatha's death, and after hearing Westley state that Agatha was possessed, she decided to fake being possessed to avoid any suspicion towards her. When Shawn and Gus visited Lucy's home, they witnessed her in her "possessed" state: acting violently, spider-walking, and speaking German. During Lucy's "exorcism," Lucy revealed a childhood fact about Shawn, which Shawn revealed that Lucy got from his internet page. Regarding the German, Lucy recited a line from her favorite movie, Run, Lola, Run.
Lucy's reveal came when the group visited Cameron's apartment and found him with Lucy, as they consummated their new relationship. Cameron was shocked to learn about Lucy's murderous actions, and after the reveal, Lucy claimed that she never meant to hurt Agatha, but also said that Agatha wasn't right for Cameron. Lucy was later handcuffed and arrested for her role in Agatha's death.