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.
A man mixed up in suspicious activity is murdered in the studio of photographer Ilmari Lavio. At the same time a charming woman has entered the studio, but Lavio does not want to report her to the police. The photographer begins to follow the beauty who calls herself Soile Mäntymaa and through her traces a league of spies.
