Commissioner Brockmann's criminal investigation is prompted by the body found by the cleaner Erna Pieper, which turns out to be very mobile! She disappears and reappears, causing considerable confusion among the survivors. The inspector and the cleaner get into a fierce competition to solve the case. The expert and the naively clever dilettante engage in a veritable battle of applied detective story logic. Which professionally proud expert likes it when a "little woman from the street" keeps messing up his work with her uneducated, "common sense" - and is successful at the same time...