"Tree of Smoke" - the name given to a 'psy op' that might or might not be hypothetical and might or might not be officially sanctioned - is Denis Johnson's most gripping, visionary and ambitious work to date. Set in south-east Asia and the US, and spanning two decades, it ostensibly tells the story of Skip Sands, a CIA spy who may or may not be engaged in psychological operations against the Viet Cong - but also takes the reader on a surreal yet vivid journey, dipping in and out of characters' lives to reveal fundamental truths at the heart of the human condition.