And as for Johnny …

… if you go mad, do you know you’ve gone mad? If you don’t, how do you know you’re not mad?

‘It wasn’t a bad film,’ Wobbler was saying. They’d been to Screen W at the Blackbury Odeon. They generally went to see any film that promised to have laser beams in it somewhere.

‘But you can’t travel in time without messing things up,’ said Yo-less.

‘That’s the whole point,’ said Bigmac. ‘That’s what you want to do. I wouldn’t mind joining the police if they were time police. You’d go back and say, “Hey, are you Adolf Hitler?” and when he said, “Achtung, that’s me, ja” … Kablooeee! With the pump-action shotgun. End of problem.’

‘Yes, but supposing you accidentally shot your own grandfather,’ said Yo-less patiently.

‘I wouldn’t. He doesn’t look a bit like Adolf Hitler.’

‘Anyway, you’re not that good a shot,’ said Wobbler. ‘You got kicked out of the Paintball Club, didn’t you?’

‘Only ’cos they were jealous that they hadn’t thought of a paintball hand grenade before I showed them how.’

‘It was a tin of paint, Bigmac. A two-litre tin.’

‘Well, yeah, but in contex’ it was a hand grenade.’

‘They said you might at least have loosened the lid a bit. Sean Stevens needed stitches.’

‘I didn’t mean actually shooting your actual grandfather,’ said Yo-less, loudly. ‘I mean messing things up so maybe you’re not actually born or your time machine never gets invented. Like in that film where the robot is sent back to kill the mother of the boy who’s going to beat the robots when he grows up.’

‘Good one, that,’ said Bigmac, strafing the silent shops with an invisible machine gun.

‘But if he never got born how did they know he’d existed?’ said Yo-less. ‘Didn’t make any sense to me.’

‘How come you’re such an expert?’ said Wobbler.

‘Well, I’ve got three shelves of Star Trek videos,’ said Yo-less.

‘Anorak alert!’

‘Nerd!’

‘Trainspotter!’

‘Anyway,’ said Yo-less, ‘if you changed things, maybe you’d end up not going back in time, and there you would be, back in time, I mean, except you never went in the first place, so you wouldn’t be able to come back on account of not having gone. Or, even if you could get back, you’d get back to another time, like a sort of parallel dimension, because if the thing you changed hadn’t happened then you wouldn’t’ve gone, so you could only come back to somewhere you never went. And there you’d be – stuck.’

They tried to work this out.

‘Huh, you’d have to be mad even to understand time travel,’ said Wobbler eventually.

‘Job opportunity for you there, Johnny,’ said Bigmac.

‘Bigmac,’ said Yo-less, in a warning voice.

‘It’s all right,’ said Johnny. ‘The doctor said I just worry about things too much.’

‘What kind of loony tests did you have?’ said Bigmac. ‘Big needles and electric shocks and that?’

‘No, Bigmac,’ sighed Johnny. ‘They don’t do that. They just ask you questions.’