Solomonsky's Circus on Tsvetnoy Boulevard is preparing a New Year's show. The performance promises to be unforgettable — a new century, the 20th, is on the threshold! But backstage at the circus there is uproar: someone has drawn a skull and crossbones on the poster… This sign — like a black mark — bodes nothing good. Illusionist Gambrini accuses the well-known animal trainer Vladimir Durov of the deed. Gilyarovsky decides to stand up for his acquaintance and unravel the affair. Durov tells him an old story about a series of mysterious deaths that occurred in the circus right in the ring. Each of them was preceded by the now-familiar symbol — the skull and crossbones. But who is he — this evil clown who has staged a truly deadly act?