William Powell and Jean Arthur star as a divorced couple who investigate a murder at a racetrack.

She and Mike North (Frank M. Thomas), the horse's trainer, persuade the reluctant doctor to investigate.

Curious, Brad opens the envelope to find a great deal of money and replaces it with some torn up magazine pieces.

When the two men start fighting, Paula tries to help using a skull she picks up, but ends up knocking out Brad instead, allowing the intruder to get away.

Police Inspector Corrigan (James Gleason) names Brad as the main suspect in the second death.

All sorts of suspects present themselves: Nick Martel (Robert Armstrong), a bookie who owed North $125,000 for a winning bet; Leroy Hutchins (Ralph Morgan), the owner of the winning horse; John Summers (Grant Mitchell), the favorite's owner; Mrs. Summers, who is seeing Martel behind her husband's back; and Summer's lawyer, Henry Strand (an uncredited Frank Reicher).

They then discover the body of Lou Pender (Paul Fix), the would-be burglar who had masqueraded as North, in a Murphy bed after he kills a spider.

Pulling out a gun, Summers admits his motive was revenge against his unfaithful wife and Martel.