Maddie Bicks (Meredith Monroe) is the villainess from Psych episode 5.08, "Shawn 2.0" (airdate September 1, 2010).
Maddie Bicks is a woman suffering from severe liver problems, but due to her alcoholism (which Maddie vehemently denies), she does not qualify for a liver transplant. However, Maddie got on the list by using the identity of her twin sister, Catherine, under Catherine's permittance. When Catherine left the country and headed to Switzerland, it made things difficult for Maddie, so the villainess decided to kill the people who were listed ahead of her, doing so by poisoning them.
Catherine found out about her evil sister's murderous actions and confronted Maddie in a parking garage. The confrontation ended with Maddie killing Catherine by shoving her into a wall which broke her skull. Though Maddie clearly felt remorse for her sister, she boldly defended killing the liver patients, stating that they had lived their lives. Maddie was later arrested for the murders.