Drury Lane, retired actor, maintains a lavish Shakespearean-themed estate on the Hudson River north of New York City. District Attorney Walter Bruno and Inspector Thumm consult him on a puzzling case.

Broker Harley Longstreet and a handful of friends took a crosstown Manhattan streetcar on a rainy night. He put his hand in his pocket, immediately collapses and dies. A cork ball loaded with poisoned needles is found in the pocket. The authorities narrow the suspects to those on the streetcar. Each companion is investigated for motive, the leading suspect being his partner, John O. DeWitt, known for having an affair with Longstreet's wife, Fern; as well as making advances to their daughter, Jeanne.

An anonymous letter arrives, promising information about the killer, who they term "X" - RM