An actress is found standing over the body of a murdered colleague from her troupe, and has no memory of what happened. The ladies were known to have been enemies. At her trial the jury decides that she is either guilty or has schizophrenia and should be hanged lest she strike again. One juror, Sir John Menier, is not convinced and, using skills he has learned from the theatre, investigates the circumstances of the case.
Sir John discovers who the real murderer is, and tries to lure a confession from him. The action comes to a thrilling climax at the circus.