An ingenious art theft takes place at Comus Towers Art Museum, and a guard is murdered in the process. Chief Ironside takes the case, but another death is to follow; this time the proprietor of the museum, who is an old friend of the Chief's.

A violin tutor at a conservatory in San Francisco is murdered, and the suspects include an eclectic mix of talented musicians. The only clue possessed by the Chief is a message sent by the dead man to one of his students, hidden in a collection of pieces of classical music.