The Empty Quarter of Arabia is the largest sand desert in the world, and one of the last wilderness areas still to be fully mapped. Sandy Gall sets out in the "camel-steps" of the great explorer Wilfrid Thesiger - across sand dunes 500 feet high and the vast quicksand known as the Mother of Poison. The temperature in the shade is degrees, and in some areas rain has not fallen for 30 years. The expertise of Sandy's Bedu guides, and his trusty camel Farha, are vital.