Eero Pursi

Tanja Bulkova arrives in Finland under the name Toini Salonen and, with the help of spy chief Rosenberg, becomes the secretary of engineer Rautavuori and discovers the drawings of a secret invention.

Lieutenant Ville Somero investigates a sabotage at a fortress site on the Karelian Isthmus in the summer of 1939. His suspicions are directed at the guests of a nearby guesthouse. Aarno Teräs an engineer leading the fortification site, and his bride Birgit Lahti get into trouble because of a band of spies and dancer Veronica Sorrento.