Influential businesswoman Ada Rudanskaya approached private detective Alexander Shibaev with a very strange request to find the first son of her recently deceased husband Nikolai. Once in her youth, Ada took Kolya away from her pregnant bride, and now, when both her husband and their common son are no longer alive, she is tormented by her conscience, and Rudanskaya wants to leave an impressive inheritance to the unknown young man. Shibaev takes up the case, and the investigation is progressing like clockwork - and witnesses have been found, and the traces have not been lost, although almost a quarter of a century has passed. It seems like we should be happy, but for some reason this state of affairs worries an experienced detective...