Beloved Vera Bethune stars as Miss Aggie in a radio soap opera, but is about to be written out. One day she drinks water from a jug and is poisoned in a murder attempt. She is taken to the hospital and survives, but the killer returns.

Fun-loving theatrical producer Spencer Lockridge invites Ellery to his mansion for a weekend of working out how to adapt one of Ellery's works for the stage. But the producer disappears shortly thereafter, and presumed murdered. A series of clues are delivered by pranksters' means. The idea is to try to get the killer to implicate himself or herself.