A medical school class attends a lecture on the psychology of crime. The unnamed lecturer (James Mason) announces that while his past lectures have covered criminals with abnormal psychology, today's lecture will focus on "the sane criminal" who may have a "strong sense of justice". He then describes the case of a murderer who is a "perfectly sane, valuable member of society", a surgeon to whom he gives the fictitious name of "Michael Joyce" (also played by Mason). The film depicts Michael's story in flashback (narrative) narrated by the lecturer, indicating to the film viewing audience that unbeknownst to the medical school class, the lecturer is telling his own story and that he and Michael are one and the same.