The Good Humor Man (movie, 1950)

Biff Jones is a driver/salesman for the Good Humor ice-cream company. He hopes to marry his girl Margie, who works as a secretary for Stuart Nagel, an insurance investigator. Margie won't marry Biff, though, because she is the sole support of her kid brother, Johnny. Biff gets involved with Bonnie, a young woman he tries to rescue from gangsters. But Biff's attempts to help her only get him accused of murder. When the police refuse to believe his story, it's up to Biff and Johnny to prove Biff's innocence and solve the crime.