On 3 May 1961, after a trial conducted largely in secret, a man named George Blake was sentenced to an unprecedented forty-two years in jail.

At the time few details of his crimes were made known. By his own confession he was a Soviet spy and rumours later circulated that his actions had endangered British agents, but the reasons for such a severe punishment were never revealed. To the public, Blake was simply the greatest traitor of the Cold War. Yet, as Roger Hermiston reveals in this thrilling new biography, his story touches not only the depths of treachery, but also the heights of heroism.

In the Second World War the teenage Blake performed sterling deeds for the Dutch resistance, before making a dramatic bid for freedom across Nazi-occupied Europe. Later recruited by British Intelligence, he quickly earned an exemplary reputation and was entrusted with building up the Service’s networks behind the Iron Curtain. And, following a posting to Seoul, he also suffered for his adopted country, when captured by North Korean soldiers at the height of their brutal war with the South.

By the time of his release in 1953, Blake was a hero, one of the Service’s brightest and best officers. But unbeknownst to SIS they were harbouring a mole. Week after week, year after year, Blake was assiduously gathering all the important documents he could lay his hands on and passing them to the KGB.

Drawing on hitherto unpublished records from his trial, new revelations about his dramatic jailbreak from Wormwood Scrubs, and original interviews with former spies, friends and the man himself, The Greatest Traitor sheds new light on this most complex of characters and presents a fascinating shadow history of the Cold War