Shawn and Gus investigate the death of Leonald Callahan, aka Diddle, a computer cryptologist who was the baritone in Gus’s old college a capella group.

When the founder of "Right Now", Santa Barbara's oldest at-risk youth program, is shot and almost killed, Shawn, Gus and a few members of Gus's a capella group from college investigate to find the culprit.