After an astonishing career as explorer and missionary, Dr David Livingstone disappeared back into his beloved Africa for one last time in search of the source of the Nile. He believed that the river sprang from four mysterious fountains which had been known to the ancient Greeks. Livingstone faced his task with unparalleled bravery but he was frail and eventually he died on the shores of a swampy lake. Over a century later, Colum Wilson and Aisling Irwin, husband and wife, retraced his last journey on foot, canoe and bicycle. They found vivid evidence of his continuing legacy to East Africa - and haunting echoes of his spirit.