A group of guests are invited by
telegram to a party at a
New Orleans penthouse by an anonymous caller. Among them are professor Murray Reid, campus radical Henry Abbott and his love interest Jean Trent,
mob boss Jason Osgood, attorney Sylvia Inglesby, District Attorney Timothy Cronin, socialite Margaret Chisholm, and writer James Daley. Upon their convergence, the guests find that each are enemies of one another. At the instruction of the anonymous host, a radio broadcasts an announcement that the guests have been brought together for a game of wits that will end in with the "ninth guest" being death itself. Shortly after, the partygoers discover a
corpse in a closet. Later in the night, Osgood dies after trying to poison the other guests. Jean reveals that Margaret recently received a letter exposing her as a
bigamist who had her husband wrongly committed to a
psychiatric hospital. Margaret, distraught over the exposure, commits
suicide at midnight. As the remaining guests argue, it is discovered that Timothy is brandishing a gun. Sylvia attempts to defend Timothy, but involuntary shoots him to death in the process before also killing herself by throwing her body against an electric gate. At 2:00 a.m., the electricity is cut, leaving the residence in darkness. In the dark, Murray is shot and Henry seriously wounded. James binds the injured Henry, believing him to be the mastermind and killer. James alleges the corpse found in the closet was that of an electrician who wired the apartment for Henry, and surreptitiously allowed him control of the radio via a switch located in Henry's chair. Henry finally admits that he is in fact the mastermind and anonymous caller who brought the group together as part of a revenge plot against Margaret: Margaret's husband was Henry's brother, and Sylvia and the corrupt Timothy aided his brother's commitment to the psychiatric hospital. After his admission, Henry allows the surviving Jean and James to depart before electrocuting himself to death. ==Cast==