In parched Port-la-Nouvelle in central Africa, Dr Mallory watches his clinic fail and dreams of discovering a third Nile to make the Sahara bloom. During the search for water, an ancient tree stump is uprooted by one of his bulldozers and water wells up, spreading until it becomes an enormous river. With the once arid land now abounding in birds and beasts, the obsessed Mallory forges up-river in an old car ferry, clashing with hostile factions as he tries to find the source of his own creation.