The Amur River is almost unknown. Yet it is the tenth longest river in the world, rising in the Mongolian mountains and flowing through Siberia to the Pacific. For 1,100 miles it forms the tense border between Russia and China. Simmering with the memory of land-grabs and unequal treaties, this is the most densely fortified frontier on earth. In his eightieth year, Colin Thubron takes a dramatic journey from the Amur's secret source to its giant mouth, covering almost 3,000 miles. A journey along the Amur by one of today's greatest travel writers.