In 1956, a Polish officer called Slavomir Rawicz caused a sensation with "The Long Walk," his account of a his dramatic escape from the Soviet Gulag and a 4000-mile trek on foot to India. The book was a bestseller and has remained in print for over half a century. Rawicz describes how he his fellow escapees slogged across the Siberian tundra, traversed the Gobi Desert and scaled the Himalayas. Along the way they faced hunger, exhaustion, disease and even a couple of yetis. A thrilling story: but was it true? Many have doubted whether this extraordinary tale can really have happened.