One of the characters is Jeff Marle, who had previously served as the sidekick in Carr's Henri Bencolin novels.

Jeff Marle, is visiting a friend at the Quayle mansion in western Pennsylvania.

A few moments after being introduced to Marle, Judge Quayle collapses after having been poisoned.

More than one poison is used in murder attempts in the household; strange shadowy figures are seen prowling the halls at night, and there is a creepy story about a marble hand that was broken from a statue of Caligula which apparently creeps around the house on its own.

After the first two deaths, a young friend of the family, Rossiter, takes a hand in detecting, with the aid of Jeff Marle; Rossiter identifies the murderer.