In the best traditions of a detective story: a confined setting, friendly people, and—seemingly—an inexplicable murder.
Young investigator Nikita, known among his colleagues as Columbo for his attentiveness and plainness, arrives at a sanatorium on the Volga to recuperate. On the very same day, a strange death occurs—of one of the important residents, Boris Solovyov, who, being practically healthy, came to visit his wife and undergo an examination. Despite the lack of any obvious motives among the suspects, Nikita begins his investigation. As he untangles the complicated relationships in the sanatorium, the investigator reaches an unexpected conclusion.
Even though everyone was nearby, one person turned out to be superfluous.