‘… And the proper name is prism. P.R.I.S.M.’ Miss Root scratched the word on the board behind her and stood back to admire it. ‘Okay? Prism. So light of all colours travels at the same speed, but just as there are big waves and little ripples in the sea, so light of different colours comes in waves of varying size …’

Billy stared at the back of Andy Weiss’s head. There was a big zit there on his neck, just above the collar of his sweatshirt. Billy watched as Weiss shifted about, the stiff stitched collar threatening to burst the zit each time they met.

‘… and when it passes through one side of the triangular prism and comes out another, it’s checked and spread out, like the rolling waves on a beach, so that all the colours appear in a rainbow band.’

The fabric won. It sliced the top off the zit and released some pale yellow liquid into Weiss’s collar. Billy watched miserably as the hand of the zit owner crept round to the back of his neck and massaged the new wound.

‘Can anyone name the colours of the rainbow and put them in order?’

Agnes Root stood with a pleasant, expectant look on her face as she surveyed her class of eighteen pupils. She glanced at her wristwatch surreptitiously to see how long it would be before lunch, and her heart skipped a little when she remembered her legs round Martin, when he had given her that thin gold-plated watch last week. She would call him at lunchtime. But lunchtime was a long way off. There was painting to get in next. The smile never left her lips as she lifted an elegant hand to Tony Spender. ‘Yeah. Tony. Want to have a go?’

Tony pushed his spectacles up on his squat nose and cleared his throat. ‘Uh, red, yellow, orange, green, purple, blue … uh … that’s it. I think.’

‘All right. Good. But you missed one and this is the order they appear in when we see them in the rainbow. Write it down with me.’

She turned to the board and started to scrawl the words below her drawing of a triangular prism. Heads in front of Billy bent to their task of copying the names of the colours in their notepads. Billy carried on staring at Andy Weiss’s neck.

Miss Root turned again to watch her class write down the colours. Only one head was up. Billy Hunt. ‘Billy? Want to write these down please?’

He continued to stare.

‘Did you hear me, Billy? Write these down please.’

A few heads looked up this time, their faces expectant, hoping for a confrontation. Billy continued looking at that neck, with its red raw zit and pus-stained collar.

Agnes Root walked to Billy’s table and bent down to his level. ‘Are you feeling all right, Billy?’

Billy nodded, not looking at his teacher.