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.

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

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.