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Alex Dennison (Robert Preston) is a playwright engaged to actress Monica Welles (Lynn Redgrave). But on the opening night of her new Broadway play, she kills herself over some bad reviews. Thoroughly distraught, Alex can't believe she'd commit suicide and begins to suspect she was actually murdered. Under the pretext of having them read for his new play, Alex invites all of the suspicious parties to an empty theater and locks them in until the truth comes out. Wikipedia