1920s London. A murder, brutal and bloodthirsty, has stained the plush carpets of a handsome London townhouse - the victim is the beautiful widow Emily French. All evidence points to Leonard, a dashing young chancer who seduced the older woman into leaving him her vast fortune before ruthlessly taking her life. At least, this is the story that Emily's distraught, devoted housekeeper Janet stands by in court. Mayhew, a penniless solicitor, is put in charge of Leonard's case.

Initially treating the suspect with indifference, Mayhew is gradually moved by the young man's case. Leonard is certain that his innocence can be proved by his wife, the enigmatic chorus girl Romaine. The entire case rests on her alibi, and Mayhew is reassured to learn that she witnessed Leonard return at 9.30pm, the time when he supposedly murdered Emily. Will she testify and save her husband, or will his infidelity make her vengeful?