The Thirteenth Chair plot
Mrs. Philip Mason commits suicide after having an affair with Stephen Lee, a dubious stockbroker, and sells her husband's securities so that Lee can buy shares. When Lee goes bankrupt, he blackmails Helen Trent by threatening to reveal the foolish love letters she wrote to him before she married. Her brother, Willy Grosby, and his fiancée, Helen O'Neil, who lives with the Grosbys, go to retrieve the letters. While Willy waits outside, Lee is stabbed to death while attacking Helen. Lee's friend, Edward Wales, tries to frame Helen for the murder by having Madame LaFarge, a psychic, conduct a séance.