Pitfall (Andre de Toth, 1948)

In Los Angeles, insurance adjuster John Forbes is a family man bored with his job and routine suburban life with his wife Sue and their son Tommy. When Bill Smiley is arrested for embezzlement, Forbes hires the private investigator J.B. MacDonald to find where the money went. MacDonald discovers that Smiley spent the money on gifts for his girlfriend Mona Stevens and becomes obsessed with her. Forbes goes to Mona's apartment to collect the gifts and falls for her. Forbes does not tell Mona that he is married and they have a brief affair until Mona learns that he is married. MacDonald has been unsuccessful in his attempts to seduce Mona and is jealous of Forbes. When Smiley is near to be released, MacDonald tells him about Forbes. On the day that Smiley is discharged MacDonald gets him drunk and gives him a gun and takes him to confront Forbes at his home so he can clear the field to Mona.