I’m staring out the window, gazing at trees. I’m 15 years old. My maths teacher is busy, untangling knots of algebra on the blackboard; my friend is taking it all down. She’s using different coloured pens, underlining, highlighting. There’s a tug in me because I know I should be doing the same.

It’s been called the letter that launched a literary genre — 16,000 amphetamine-fueled, stream-of-consciousness words written by Neal Cassady to his friend Jack Kerouac in 1950.