In Madrid, during a popular festival, Don Paco, the owner of a freak show called The Palace of Wonders, has to deal with the demands of Levinsky, a sinister character who apparently has something to hide…

Federico is having an affair with Fernanda, which he believes widow, when in fact she is married. When the trick is discovered, a doctor appears very opportunely saying that infidelity is a disease caused by bacteria and has no cure. In his private clinic he applies a treatment that consists of locking up every adulterer with his mistress.