The engineer Douglas Maclean, Princess Shirvinskaia and her lover Rumanesku arrive in the Soviet Union as members of the circus troupe and fight against the country covertly. Rumanesku starts working at the oil refinery with the different name. Here he gets acquainted with Misha Petrov, one of the Red Devils who works on some important military invention. Rumanesku uses the favorable moment and steals Petrov’s drawings. Tom Jackson becomes a witnesses of this crime by accident. He chases Rumanescu and discovers that the subversionist „worker“ Jon and the circus artist are one and the same person. Tommy informs his friends about this discovery. Misha, Duniasha and Oksana together with militia officers chase the subversionists who are about to flee abroad. At the Turkish border the subversionists are killed in the avalanche.