Set the Piano Stool on Fire reveals the relationship between a master and his prodigy

Set the Piano Stool on Fire, already picking up an unofficial following and due to get its public premiere at the Curzon Mayfair next month, is one of the most fascinating films about pianists ever made. One of its protagonists is caught in the act of bowing out (at 80) after a long career as (arguably) Beethoven's leading exponent, the other is coming in at 18: the tutorial relationship between Alfred Brendel and Kit Armstrong is fraught with significance.

Brendel first heard Armstrong play five years ago, and his gentle remark that he "would like to hear the boy play more" led to a series of lessons which is still ongoing. He was mightily intrigued, as everyone else is when they encounter the diminutive British-Taiwanese genius. Because genius really is the word: he's not only a pianist and composer, he's also jumped through all the mathematical hoops Imperial College has to offer, 10 years ahead of other students of his age; he's a born philosopher, a killer on the tennis court, and one of his hobbies is making origami of mind-boggling complexity.

But the matter of Mark Kidel's film is Beethoven and Schubert, on whose music Brendel is the fount of all knowledge. And to watch the old man demonstrate with graceful theatricality a Schubertian gear-shift – reproduced with variations by the bright-eyed pupil – is to learn something new about the music as well. Brendel is dazzled and bemused by Armstrong, but he makes one caveat: "He must keep his childlike quality." It's pretty clear the impish Armstrong will.

'Set the Piano Stool on Fire', Curzon Mayfair, London W1 (0871 703 3989) 4 June, 6pm