In 1980 Stephen Pern went for a walk in West Africa. From the papyrus choked shores of elusive Lake Chad, Pern and his Nigerian companion, Waziri, wander south, hopscotching the international border between Nigeria and the Cameroons. The lake and the fringes of the Sahara behind them, they cross featureless savannah and baking plain until they reach the Mandara Mountains. They traverse the entire length of the hill chain until they reach the River Benue, paddling across in a dug-out canoe. For company there are two donkeys and occasional guides who lead the way to the next village but seldom beyond. The route is by tracks which avoid wheeled traffic and which connect a still traditional world, part Islamic, part pagan, where medicinal vulture's feet mingle on market stalls with transistors and strident cassettes.