The Mark of Cain is a 1947 British drama film directed by Brian Desmond Hurst and starring Eric Portman, Sally Gray, Patrick Holt and Dermot Walsh.

Dr. White is suspicious of the circumstances behind John's rapid decline and suspects poison, but doesn't realise that it is Richard who is slowly killing his brother, while fomenting suspicion of Sarah with the servants and the doctor.

John suddenly realises what is happening and tries to call for help, but Richard holds his weakened brother down on the bed and, before placing a pillow over his face, informs him that he will have Sarah accused of his murder, then, when he saves her, she will be so grateful that she will do anything he wants.

Richard had also planted small traces of arsenic in Sarah's things, and the doubts he had deliberately implanted in the servants' minds are used against her, as is the false suggestion that she was having an affair with Jerome, the son of business associates of John's.

Eric Portman is quite good as the vain egoist, Richard; Sally Gray is not very interesting as Sarah; and Patrick Holt is not happy as the boorish John.

Played against phoney late nineteenth-century Manchester backgrounds, it tells, as far as we could gather, of the machinations of a ranting megalomaniac, but fails completely to make its point, if any, clear.

Dermot Walsh and Patrick Holt overplay their roles and both were a promise never really to be fulfilled, but Eric Portman dominates the film in a barnstorming acting performance.