In case you were wondering, I don’t know much about the ‘theory’ of time travel, or the rules, or what you can and can’t do.

I don’t think anyone does, really.

I’ve heard of the ‘Grandfather Paradox’, which says that if you go back in time and murder your own grandfather (nice) then you cease to exist, supposedly, because if he’s dead he will not have fathered your dad, and he in turn will not have fathered you. And I know about Dad’s Law of Doppelgangers, because he told me about it. But I don’t know much else apart from watching bits of Star Trek and Dr Who and in those it seems like anything goes, which is handy for the writers, I suppose, but doesn’t help me at all.

And besides – who invented these ‘rules’? So far as I can tell, it’s all theory – no one has tested anything, although it seems as though Dad’s Law Of Doppelgangers is holding up pretty well to real-life experimentation.

So I don’t know what to expect. I just know I’m relieved as anything when the haziness in my eyes clears, and I’m still in the bunker, but there’s no man trying to get in.

I get out of the tub and sit in the desk chair for a minute, letting Alan Shearer run over my hands. He seems pleased to see me, at least. I pop him in a drawer under the bunk bed while I work out what to do next.

What has happened with that man, Graham? He will have entered the bunker, and he will have seen that the light was on, and the swivel chair turning around, but nobody there at all. How spooky will that have been?

Of course, the sensible thing to do, now that I’ve got Alan Shearer, would be to head straight back to what I have begun to think of as ‘real time’, and Grandpa Byron, waiting in the cafe. After all, if I don’t come back straight away, he’ll start to get worried and come looking for me.

Trouble is, of course, I can’t: Graham is waiting there. It’s like I’m trapped in a sort of time-cupboard in the garage: as soon as I come out, Graham will see me.

My first thought is to set the return time to the present to just a minute before I reached my old house, coming from the fish and chip shop.

But that is a direct violation of Dad’s Law of Doppelgangers. If it was possible, I would bump into myself heading into the garage, and as I have just discovered, the time machine won’t permit that.

The other option is to set the return time to a little later, say twenty minutes, and hope that, by then, Graham and Bella have stopped stalking the garage looking for an intruder. Except that wouldn’t work either. The pesky doppelganger thing means that I – or a version of me – am already there.

I admit it: I’m stumped. Sometimes, though, when you have to think of an answer but none will come, you just need a little time.

Meanwhile, I can’t resist taking another look at 1984.

I come out of the cellar and into the daylight again.

It’s still Radio One playing, and the same presenter, and I can hear him say, “It’s eleven twenty-three here on Radio One, and this is Cyndi Lauper with Time After Time …”

In the garage everything is the same, but there’s no sign of little Stokoe or his mum.

Outside, I feel even more nervous than the last time I was here, as if someone might recognise me. Daft, I know, but that’s how it feels.

And here comes not-all-that-old Mr Frasier, walking in the other direction this time, away from his home. I decide to try something.

“Excuse me,” I say. “What year is it please?”

He glances down at me, but he barely even stops. “Get awa’ wi’ ye,” he says without removing the pipe from between his teeth. “Y’cheeky wee sod,” and he strides on past.

Strange, I’m thinking. But then, I’m dressed differently from the last time, I think I phrased the question differently last time too, Sunday-best polite, and so he reacted differently.

I carry on down the alleyway thinking about the last time. Did it exist? It did for me but did it for Mr Frasier? Was he rude to me because I had already asked him the same question an hour ago? Or am I in a completely different 1984?

And if that lot wasn’t enough to make my head spin, as I carry on walking down the alleyway, what happens next puts it in actual danger of just going, like, BOOOM!

I meet my dad.