Shawn, Gus, Lassiter, and Woody wake up in the Psych office with no recollection of what happened the night before. When a body shows up dead, the quartet conduct a discreet investigation in order to exonerate themselves and find the real killer.

A local drug syndicate known as the Caminos falls under attack by a masked vigilante called The Mantis, and Lassiter is soured by this since The Mantis has already made more progress than the police. Shawn is also put off, due to Juliet expressing an admiration for The Mantis' efforts. Shawn and Gus believe that a new cop is the vigilante, but as they put the pieces together, they start to believe that the Mantis' efforts may not be altruistic.