The author reflects on his own fifty-year voyage of discovery of Asia, culminating in a journey to far western China in 2018; to Dunhuang, the oasis town on the fringe of the Gobi and Lop deserts that for centuries gave access to the Silk Roads - and to the 'Caves of a Thousand Buddhas'. These temple-caves once concealed the world's oldest printed book, known as the Diamond Sutra, but as he contemplates the significance of the missing sutra and an empty cave, he finds himself confronted by the world's oldest question.