Professor Bogolyubov's newly designed airplane attracts the attention of participants in the May Day parade in Moscow. It flies higher and faster than all others. That same day, foreign intelligence agents and an experienced spy disguised as a clown head to Bogolyubov's dacha, where he is staying with his wife and children. But the designer's plans will not fall into enemy hands, because state security lieutenant Mikhailov is keeping a close eye on the spies' activities…
