Leningrad, February 1942. A German air raid has destroyed Block A of the Institute of Experimental Medicine where lethal viruses are researched. The containers with those viruses have disappeared. Severe frosts prevent the outbreak of an epidemic in the besieged city. However, spring is approach- ing and the thaw will set in soon. A young lady doctor, Maritskaya, and an NKVD officer have only 72 hours to prevent a disaster. Life and death, love and betrayal are interlaced in the rapidly unfolding events...