Long before she distinguished herself as a director, Mai Zetterling was the star of several moody melodramas.  Based on a novel by Elizabeth Myers, the film casts Zetterling as Mrs. Carol Edwards, whose husband lies in a hospital bed, afflicted with asthma.

Mrs. Edwards becomes a murder suspect when blackmailer Mr. Sine (James Robertson Justice) is killed on the hospital grounds.  Since the film is not a mystery, it is safe to reveal that the genuine killer is Mrs. Christopher (Fay Compton), the hospital's wealthy patroness.  Basically a character study, Blackmailed spends most of its time delving into the personal problems of Mrs. Edwards and the other suspects.