A man working at the Pym's Publicity agency falls to his death. Lord Peter decides to go under cover at Pym's publicity to find out who killed Victor Dean.

Lord Peter attends a fancy dress party and learns the details of a drug ring.

Lord Peter discovers that Dean's girl friend has a drug habit and decides to take on a further alter ego - as his own cousin.

There are already two dead bodies and Lord Peter may soon be the third as it becomes clear that the gang smuggling drugs is using the advertising agency in a complex plan to deflect suspicion.