Fun-loving Miri is a genius with numbers. She puts this talent to good use in her job at the town bank in the small village of Hattenstein, where she actively helps her often overburdened boss. When a local winegrower is found dead in a wooded area, she also develops a penchant for detective work. The policeman Nils, one of her old schoolmates, believes it was a sudden heart attack. But Miri's extraordinary powers of deduction tell her that there is something fishy about the case. With the moral support of her ownerless dachshund, Frauchen, she uncovers a large-scale crime in which even the mayor of the town seems to be involved.