In the summer of 1941, German troops surrounded the Russian city of Leningrad - now St Petersburg - and began the longest blockade in recorded history. By the most conservative estimates, the siege would claim the lives of three-quarters of a million people. Most died of starvation. At the centre of the embattled city stood a converted palace that housed the greatest living plant library ever amassed - the world's first seed bank. After attempts to evacuate the collection failed, and as supplies dwindled, the scientists responsible faced a terrible decision: should they distribute the specimens to the starving population, or preserve them in the hope that they held the key to ending global famine? 'The Forbidden Garden' tells the remarkable and moving story of the botanists who remained at the Plant Institute during the darkest days of the siege, risking their lives in the name of science.