Kirk Bennett is falsely sentenced to death for killing blackmailer Mavis Marlowe, ex-wife of nice-guy drunk Martin Blair. Bennett’s stand-up wife Catherine tries to prove him innocent, enlisting the aid of Blair, who falls in love with her. Bennett’s execution draws near as the two pose as piano player and singer, trying to get the goods on sleazy nightclub owner Marko, a prime suspect. Failing to nail Marko, Catherine goes off to meet with her husband, scheduled to die the next morning, and Blair slips into an alcoholic stupor before the real killer is revealed.
Black Angel begins as we zoom up to a swanky apartment building in Los Angeles as Marvis Marlowe (Constance Dowling) is primping and berating her maid for putting the wrong music on the phonograph. The recording of the song Heartbreak reminds her of her musician husband Martin Blair (Dan Duryea) who wrote the song and is standing downstairs barred from entering by the doorman. When Martin sees the doorman allow Marko (Peter Lorre) up to Marvis apartment he gives up and walks away. Martin and Marvis were married at one time but now she refuses to meet with him which causes emotional reactions in Martin so great that he goes on a drunken bender before going to his current piano-playing job at Als Place, a local saloon. When Martins best friend and custodian shows up, he takes the hapless musician away and locks him in his apartment to sleep it off. In the meanwhile Kirk Bennett (John Phillips) goes to Marvis apartment and discovers the femme fetale dead on the floor and the seeming presence of someone just exiting the apartment. Kirk is held for the murder in the case led by detective Capt. Flood (Broderick Crawford) who can only find a heart-shaped brooch missing from the dead womans apartment. After a trial Kirk Bennett is convicted and is sentenced to execution. Kirks wife Catherine Bennett (June Vincent) goes into action believing that her husband is innocent of murder she tracks down Martin and confronts him about his actions on the night his ex-wife was murdered. Catherine is dismayed when she learns of Martins alcoholism and his obvious emotional vulnerability in regards to his murdered wife, but what really convinces her that he is innocent is that he was locked in his apartment at the time of the murder. Martin decides to help Catherine because he remembers Marko entering the apartment and thinks he may be the murderer. Martin and Catherine concoct a scheme to get a job performing at Rios, the club Marko owns in hopes of getting more information on Marko that may lead to showing that Catherines husband is innocent. They begin finding clues of Markos relationship with Marvis, many of which are secured in a safe in the night club. During this Martin has developed a real connection with June and confesses his feelings for her, but when she rejects him because of her determined belief of Kirks innocence, Martin goes on a drunken bender. When Martin sees a woman wearing the missing brooch from Marvis, he realizes that in an earlier drunken stupor he had given it to her, and the details of the murder slowly become clear.