Diana Baring, a young actress, is found at the scene of a murder with no memory of the night in question. Despite her protests of innocence, she is arrested and charged with the crime. Her case goes to trial, and the evidence against her appears overwhelmingly damning, leading to her conviction. During the trial, juror Sir John Menier, a distinguished actor and playwright, is struck by doubt concerning Diana's guilt. Intrigued and unconvinced by the circumstantial evidence, Sir John decides to investigate the case independently after serving on the jury that finds her guilty.

As Sir John delves deeper into the particulars of the case, he encounters a slew of intriguing characters within Diana's theatrical troupe. Each person seems to hold a secret or harbors a motive that could explain the strange circumstances surrounding the murder. Through sharp investigation and psychological insight, Sir John begins to unravel a complex web of jealousy, passion, and deception that extends beyond the initial crime scene. His pursuit of truth takes him through a labyrinth of twists and turns as he races against time to uncover the real murderer before Diana faces her grim fate.