When a man is found dead in his private sauna, Inspector Rivera and Rex investigate the suspicious circumstances in which the sauna door was jammed shut, causing the man to suffer a heat-induced heart attack. Soon Rivera finds that the man's mistress, his brother and his girlfriend all had a motive to kill him.

The illegitimate daughter of a wealthy man becomes the target of her half-sister's plot to kill her to avoid sharing her father's inheritance. Not knowing why she has been targeted, the girl goes into hiding. Meanwhile, Inspector Rivera and Rex set out to find the missing girl.