Psych - Season 2: Episode 14

Henry bails on his weekend outing with Shawn, stating that he's too ill to leave the house. Shawn is nowhere near upset until he and Gus catch Henry driving by, clearly not sick at all. Naturally, they follow him and discover he used to be a member of the Monarch Lodge, a clandestine society. They barge inside looking for an explanation and are surprised to find one of the Lodge members lying dead before them. Shawn suspects murder, and in order to conduct an inside investigation, he becomes a member of the society.