Book excerpt: 'That great blue Sphinx', Debussy called the sea. Debussy himself was something of a Sphinx: in the early 1890s he was thinking of 'founding a society for musical esotericism', and although, on the surface, most of his music is instantly engaging and accessible, at a deeper level run currents that are dangerous, unpredictable, destructive. In this new biography, Roger Nichols considers the life and music of this seminal figure charting the currents and the whirlpools in which other humans were sometimes unlucky enough to get caught. Debussy's status is such that no modern composer has been able to ignore him, asking, as he does, any number of riddles to which late twentieth-century music is still searching answers.