A young unemployed man gets a job as a private secretary by chance. A good salary, a first-class apartment - but things are not going right in his new residence. Notes warn him, a beautiful woman appears in the mirror, valuable documents disappear from the tightly locked safe.

All is not well in the Mollheim home. The elder Mollheim decides to marry off his daughter with an unusually large dowry, in exchange for a rare Chinese idol. The daughter of the house, being opposed to the idea, decides to hire a private detective to get to the bottom of it. The detective doesn't get far before the idol is stolen and its owner is murdered.

Every Friday the 13th, a member of the Eulenstein family dies. The son of the most recent victim hires a detective to investigate.