Darrow Nash is a private investigator, hired by a woman named Alice McKenzie to dig up evidence of her husband Mac's affair so that she can divorce him. On a fateful night, he shows up to the apartment kept under his secretary Teresa Vail's name to grab some photographs of Mac and her together, but instead finds the two dead inside, Mac with an extension cord around his neck and Teresa with a bullet hole in her head. The police, Alice, Teresa's mother, and a redhead all show up to the crime scene.

Alice fires Nash, thinking the case closed as a murder-suicide. However, Nash thinks there's more going on, and goes to Teresa's mother's place, where he finds the redhead and the mother living together. The mother asserts that there was no way Teresa had killed herself, and the redhead, Eileen, explains that Teresa and Mac hand't been sleeping together. They speculate that perhaps Paul Devore, who worked with Mac, might've had a motive, the two having had a rivalry of sorts. Eileen comes on to Nash, but Nash leaves.

He goes to the McKenzie house and breaks in, finding a box of photographs of Mac with various men, and some threatening notes. Alice and Paul show up before he can get out, so instead he confronts them. He exposes Paul's sexual harassment of his secretaries (Eileen had been his secretary before quitting due to this), leading Alice to break up with him. Alice seems to have no idea of Mac's sexuality. Next Nash goes back to the scene of the crime, hoping to catch the police still there so he can hand over the evidence he procured from the McKenzie house. Instead he finds Eileen in the apartment. She tries to seduce him to distract from her guilt—but he gets her to confess that she and Teresa had been trying to extort Mac, but when they got to the apartment they'd found Mac already dead, swinging from the doorway, and in Teresa's fear the gun had gone off, killing her.

After Eileen confesses, Paul Devore shows up, pointing a gun at Eileen, blaming her for Teresa's death. But Nash realizes that Paul is the true culprit. He used his relationship with Alice as an alibi, found out Mac was gay, and used Teresa to get the two girls to try to extort him. But he told the girls and Mac different meeting times, giving himself an hour to kill Mac and take the money before the girls showed up. He'd pinned Mac's medals of honor from the war onto his jacket, part of his jealousy towards Mac, as Paul had shot himself in the foot to get out of the war. Paul and Eileen shoot each other, Eileen having had no idea of his involvement in the scheme.

Eileen lives, despite a gunshot wound to the chest. Nash goes home and looks over his own medals of honor from the war, thinking about how his own bravery was a form of acting, hiding his fear. In the end, Nash and Eileen go free in court, but Nash still harbors his suspicions about Eileen's guilt.