Police Lieutenant Leonard Diamond is on a personal crusade to bring down the sadistic gangster Mr. Brown. He is also dangerously obsessed with Susan Lowell; she is Mr. Brown's girlfriend, and is despondent and suicidal because she cannot escape from him. Building his legal case against Mr. Brown, Diamond's main objective becomes investigating the identity of a woman, known only by the name "Alicia", who is connected to the gangster. Mr. Brown becomes exasperated with Diamond's investigation and, with his
second-in-command McClure and thugs Fante and Mingo, kidnaps and tortures the lieutenant, and pours a bottle of alcohol-based hair tonic down his throat before letting him go outside his police captain's apartment. Diamond eventually learns through one of Mr. Brown's past accomplices, Bettini, that Alicia was actually Mr. Brown's wife. Bettini suspects that Alicia was sent away to Sicily with former mob boss Grazzi, then murdered, tied to the boat's anchor, and permanently submerged. Diamond questions the operator of an antique store bankrolled by Mr. Brown named Dreyer who was also the skipper of the boat. Dreyer denies involvement and refuses to disclose anything to Diamond, but is nonetheless murdered by McClure shortly after leaving his shop. Diamond tries to persuade Susan to leave Brown and admits he may be in love with her. He shows her a photo of Mr. Brown, Alicia and Grazzi together on the boat. Susan finally confronts Mr. Brown about his wife and is told she is still alive in Sicily, living with Grazzi. Mr. Brown orders a hit on Diamond. However, when Fante and Mingo go to Diamond's apartment, they mistakenly shoot and kill Diamond's burlesque dancer girlfriend Rita instead. Diamond sees an up-to-date photo of Alicia but realizes it was not taken in Sicily due to the presence of snow on the ground. This leads Diamond to suspect Mr. Brown had killed his boss Grazzi, and not Alicia. Diamond tracks Alicia to a sanitarium, where she is staying under another name. He asks for her help. Meanwhile, McClure wants to take over. He plots with Fante and Mingo to ambush Mr. Brown, but they betray him. With McClure dependent upon a hearing aid, Mr. Brown promises, as a small mercy, he will not have to hear the bullets when they murder him. Brown removes the hearing aid, at which point the soundtrack abruptly cuts to complete silence, and Fante and Mingo gun down McClure in a brief subjective silent shot. At police headquarters, Susan and Alicia talk, and Diamond tells them about Rita being murdered. Alicia agrees to tell everything she knows, but Mr. Brown shows up and Alicia reacts with terror when she sees him. He has a writ of
habeas corpus, effectively preventing Alicia from testifying against her husband. Mr. Brown takes food to Fante and Mingo, who are hiding out from the police, and also gives them a box, saying it contains a large sum of money for them to divide between them, but the box contains a bomb that apparently kills both of them. Mr. Brown shoots Diamond's partner, Sam, and kidnaps Susan, planning to fly away to safety. However, Mingo survives the assassination attempt by Mr. Brown, and he confesses to Diamond that Mr. Brown was behind all the murders while sobbing over the body of his colleague Fante. Alicia is able to help Diamond figure out that Mr. Brown has taken Susan to a private airport where he intends to board his getaway plane. However, Mr. Brown's plane does not show up, with the situation culminating in a foggy hangar shootout. Susan shines the
fog lamp from Mr. Brown's car in his eyes, dazzling him and allowing Diamond to arrest him. The final scene shows the silhouetted figures of Diamond and Susan in the fog. ==Cast==