Brother and sister Danya and Valya move with their mother to a northern seaside town and immediately become participants in an exciting but dangerous adventure.
| Actor | Role |
|---|---|
 Nikolai Volkov St.Foma Konovalov | Foma Konovalov |
| IInna ZhuravelGlafira | Glafira |
 Aleksey ZaytsevPasha Zhgutov | Pasha Zhgutov |
| TTanya DemushkinaValya | Valya |
| YYura BondarenkoDanya | Danya |
| YYura LeshovGrandson Foma Konovalov | Grandson Foma Konovalov |
 Valeri YurchenkoStepan Novoselov | Stepan Novoselov |
 Raisa KurkinaNatalya Yevgeniyevna | Natalya Yevgeniyevna |
 Sergey BobrovSkornyakov | Skornyakov |
 Ivan VoronovForeign Ship Captain | Foreign Ship Captain |
 Elena MaksimovaMarya Stepanovna | Marya Stepanovna |
 Pyotr SavinPyotr Mikhaylovich | Pyotr Mikhaylovich |
 Ivan ZhevagoForeign Ship Skipper | Foreign Ship Skipper |
| PP. MakarovRadio Operator | Radio Operator |