The owner of a used bookstore, Fyodor Bukolev, found notes from a certain Victor in one of the books. He witnessed a crime and openly fears for his life. Having rushed to search, Fyodor learned that Victor had recently died. Or perhaps he was killed. The dead man's sister Marina makes an indelible impression on Fyodor, and he frivolously gives her his word to find the killer. The investigation takes him behind the scenes of a small theater in the capital, where Fyodor finds a like-minded person, director Tarasov, a passionate and unpredictable man. Meanwhile, in the theater, the investigation of another crime is in full swing - the murder of two young actresses. Investigator Zimin, leading the case, decides: a couple of amateur detectives can be given some freedom. It doesn’t even occur to him that these two are capable of bringing to light a sophisticated criminal who has eluded himself over and over again...