Over 1,500,000 people died from starvation and disease when Germany besieged Leningrad for 900 days in one of the Second World War's darkest episodes. But even when the Soviets forced the Germans to surrender, Joseph Stalin secretly purged the city, executed the very people whose bravery had ensured its future and imprisoned their families. The documentary series draws on hitherto classified Russian documents and survivors' testimony to explain the dictator's actions.