This is a tale of two men of the same age (we first encounter them at sixteen), and our narrator, their elder.
The younger pair are classmates at a music academy. One, Paul, is a scholarship boy, thrusting through from a hard-scrabble background, rather chippy, overwhelmingly gifted, a virtuoso with a short temper. The second, Jonathan, is richer, less gifted, less driven, less attractive. He leeches on to the wunderkind, and uses him to win access (or proximity) to fame, genius, obsession and all the people who come to stare at these things.
They both fall into the orbit of the narrator, a tutor who nurtures Paul's gifts lovingly and carries a torch for him at the same time. Jonathan uses his riches to feed Paul's increasing need for illicit substances, thinking he can control him better, keep him close, by these means. This strategy works up to a point, but boils up and over.
Meanwhile our increasingly unreliable narrator prompts us to reconsider our presumptions and, swiftly, scarily, the book whips to its close and its entirely surprising outcome . . .