The film takes place during the full-scale Russian invasion of Ukraine. After the Kakhovka dam is blown up, a detachment of Ukrainian soldiers led by a female fighter with the call sign Mara finds themselves in a secret Soviet bunker at the bottom of a reservoir where the USSR conducted human experiments during the Cold War. The consequences of these experiments are still in the bunker in the form of the half-living corpses of Soviet soldiers. Now, in order to survive, Ukrainians need to defeat the Soviet zombies, their own fear, as well as overcome internal disputes and trust each other.