Everyone loves Tchaikovsky's music – except musicologists, who mostly regard him as a provincial also-ran to Mozart, Beethoven and Brahms. Roland John Wiley's persuasive musical analyses should go a long way towards curing that professional myopia, but with this oddly elusive composer there are biographical misconceptions – notably surrounding his death – which need to be shifted first. Popular myth, reinforced by feature films, has him arraigned for sodomy, at the height of his fame, by a kangaroo court of his peers, and obediently swallowing poison. Cholera – the official cause of his death – is for some too unsatisfyingly bland a solution.

The suicide theory, lovingly glossed by amateur psychology, even prevails among some of the composer's musicological champions, who were outraged by a recent Russian biography presenting him as merrily cavorting in gay bathhouses: "The outing of Peter Ilyich" thundered a review in the New York Times. But as Wiley makes clear, Tchaikovsky was out from the start. "Can you really, most beloved woman in my harem, young and beautiful Klimena, doubt my love for a single moment?" he wrote to his student friend Ivan Klimenko. "My beauty is a gymnasium student, and must finish her examinations," he later wrote of another boy who had taken his sybaritic fancy. And that fancy roamed free: Wiley's narrative is studded with crushes on coachmen and servants, and threaded through with Tchaikovsky's unconsummated passions for a violin student, and his adored nephew, Bob Davidov.

One of Tchaikovsky's effusive letters to his brother Modest signs off with a camp feminisation of his own name: "Your devoted and loving sister, Petrolina." Moreover, the imperial court was relatively relaxed about homosexuality, and Tchaikovsky's massive state funeral should have belied notions of a furtive death. And Wiley shows that in his final year, the composer – having realised his artistic ambitions, and watching his friends die one by one – was tying together the loose strands of his life, gracefully anticipating the end. The suicide theory doesn't fit the facts.

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But Modest was homosexual too, as was their brother Anatoly, and expurgating Tchaikovsky's letters after his death was their clumsy attempt to doctor the family record. Indeed, the chronically self-doubting composer intermittently urged them to fight their sexual proclivities: his sudden decision to marry was his own attempt to straighten his image. The story of his escape from that unconsummated relationship – repeatedly paying off his wife, who became his stalker – is both comical and sad.

Wiley's belief that Tchaikovsky's sexual orientation was of central importance (including to his music) leads his narrative along fruitful paths. And the composer himself recognised this truth, itemising the traits caused by his "buggermania": "an estrangement, fear of people, shyness, immoderate bashfulness, mistrust..." He was, by all accounts, the kindest friend, as well as being a phenomenally prolific creator, conductor and teacher.

But everything boils down to his unique musical voice, which a contemporary critic described as "that noble tone, devoid of the commonplace... that somewhat feminine softness". Noting that Tchaikovsky followed no manifesto, avoided alliances, and formed no recipe for others to follow, Wiley uses the Russian word prelest to pinpoint the quality which singles out his music from all others, commingling "charm", "seductiveness" and "fascination". Presenting life and art as parallel but separate strands, this coolly magisterial book scotches myths, accepts that some mysteries may never be solved, and builds up a picture of this profoundly conflicted man, and his wondrous music, which will probably never be bettered.