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 Yoless.

"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 Yoless 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 Yoless, 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 Yoless. "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 Yoless.

"Anorak alert!"

"Nerd!"