Manville Moon is a private investigator. On a night out with his girlfriend Fausta Moreni, the lovely owner of the El Patio Cafe, a group of customers invites them both to a private party at an inventor's home, to celebrate the launch of a business venture based on his new device. But soon after their arrival, the inventor is shot dead by an unseen assailant. Police suspicion quickly falls on the boyfriend of one of the guests, and Moon is hired to prove his innocence - plunging him and Fausta into deadly danger...