A historical spy thriller about an Estonian Military Intelligence (O-2) officer, who has to track down a mysterious Soviet double agent. The story begins in 1937 when our protagonist Feliks Kangur is the Head of the Soviet Section. As a spy with an art history education, he still attends various professional events for his own enjoyment. At one of these conferences, Feliks meets the young Polish art historian Maria and falls in love. Suspecting that she is working for Feliks, the Soviet secret service arrests Maria, who’s unaware of Feliks’ spy background, and tortures her to death during a merciless interrogation. This catastrophe leads Feliks to step down and to move to Finland, where he takes an insignificant job at the Estonian Embassy. Two years later, August 1939. Europe fears an imminent war and Estonia is alone in opposing the aggressive Soviet Union. Feliks’ successor to the post of the Head of the Soviet Section gets brutally killed. After this mysterious death, the boss of O-2 finds out from his Soviet source that there’s a double agent in the midst of them. He decides to bring Feliks back from Finland to uncover the Soviet mole. At the same time, other events start to unfold at a dizzying speed. The Soviet Union and Germany sign a non-aggression pact and divide Europe into spheres of influence, leaving Estonia, Latvia, Lithuania, and Finland to Stalin. After arriving in Estonia, Feliks focuses on three main suspects who worked under the murdered officer. However, once all the potential suspects start turning out to be innocent, Feliks starts looking into the source who had the information about the mole – the Soviet diplomat Ivan. It’s becoming ever clearer that the Red Army is working with the Soviet military intelligence to bring about the occupation of Estonia under a top-secret plan called “Volcano”.