The series is based on a "true story" of a Russian spy Colonel Isaev (Stirlitz) in Nazi Germany during 17 days at the very end of WWII. Stirlitz has worked his way to the very top of the Nazi hierarchy without being discovered. However, his "colleagues", top Hitler's officers Borman, Mueller and Schellenberg are beginning to suspect him. Stirlitz is constantly walking on the edge between his two identities, sending information to Russia, while skilfully maintaining the appearance of a loyalist to the Nazi regime.