Standing outside the vet’s, the absolute lunacy of handing over my mobile phone to Macca has begun to seep into my head and I comfort myself (very slightly) with the knowledge that there wasn’t much battery life left, and he won’t be able to do much with it. But I will have to get it back, I know that.

I’m also now very keen to get back to my world, my time. The idea of flipping between the two as I wish, of setting destination and return times according to convenience, is something I’m only just becoming familiar with, and I’m very, very far from relaxed about the whole thing. You’d be the same. No one is born with an instinctive understanding of multi-dimensional time travel. Not yet at any rate. There’s also the risk element. It’s the breaking in, sneaking around, lying, hiding and stealing stuff that’s doing my head in, as much as the time travel itself. (Mind you, the time travel would be enough on its own, believe me.)

I wait till Macca and Pye have headed up the road away from the house and there is no one around in Chesterton Road. Then I head back to the bunker under his/my house.

Remember, several hours ago but thirty years in the future, I had only just escaped being found in this same bunker by Graham, who was trying to force the door.

I’d had the brilliant idea of using the time machine to escape imminent danger. Brilliant, cunning … and completely stupid. Because I’m now sitting in front of the laptop with nowhere to go.

Returning before I had left was a non-starter because of Dad’s Law of Doppelgangers. Remember? I would risk bumping into myself and that’s not possible. And returning after I had left doesn’t work either – for the same reason.

That leaves the option I had rejected before as Graham was forcing the metal door: find somewhere to hide in the bunker and I would have only seconds to do it. I scan the layout of the little underground room. There’s only one possible hiding place, and it’s pretty pathetic.

I set the time coordinates for the time I left.

And then I hesitate, going through all the what-ifs I can think of. What if Graham just waits by the door? What if he locked the door from the outside? The main one, of course, is: What if he finds me … what if … what if …?

Sometimes, despite the what-ifs, you just have to act. I can’t be here forever, driving myself nuts with indecision. Instead, reclaiming Alan Shearer from the drawer and stashing him safely in my hoodie pocket, I climb into the tub, grip the laptop tightly, and press ‘enter’.

Seconds later, I’m back where I left. I can again hear the pieces of broomstick clattering to the floor, and the wheel that opens the door is turning rustily. One piece of wood remains stuck, jamming the door’s mechanism for a vital few seconds as I climb out of the tin tub and hit the light switch just as the final bit of wood gives way.

“Careful Graham! There might be a gang of them!” I hear Bella say as he pushes the door open.

There are five stairs leading down into the bunker from the doorway and all I can do I crouch in the space beneath them.

I know – I told you it was pathetic, right? Worse, the steps are made of grid metal like you see in factories and if he looks straight down, Graham will see me crunched up in a ball, eyes screwed tight shut as if that could make a difference to whether or not he sees me.

Half opening them, I see a shaft of dim light coming from the doorway and falling on the laptop and tin bath. The laptop is closed, but between the keyboard and the screen is a thin line of light because it hasn’t powered down properly yet. Can he see it? I can’t tell. He’s crouching by the opened door because at the top of the stairs there’s not enough head room to stand up properly, and his feet are directly above me.

“Hello?” he calls. “I know you’re in there. You’d better come out or you’re in trouble!”

He’s scared. I can tell from his voice. Then his feet move and he starts to come down the metal steps.

“Don’t go in, Graham. Come back, love.”

He stops, and I have an idea. Silently, I take Alan Shearer from my pocket and gently release him on to the floor, where he scampers across the patch of light behind the tin tub. He’s only visible for a moment, but it’s enough.

“Oh my God, Bella. There’s rats down here.”

“Yup,” I think to myself. “Rats for babies,” and I think I even smile a bit, remembering Carly’s sly put-down.

Bella’s voice has taken on a harsher tone. “Graham. Come away now. You’ll catch something if they bite you.”

His footsteps move back up the stairs and I hear him say to Bella, “Come on love, we’ll call the police.”

“And the council. We need the pest-controllers.” I hear the door between the kitchen and the garage click shut and only then do I realise that I have been holding my breath for pretty much the whole time.

Seconds later, I’ve scooped up Alan Shearer and I’m out of the bunker, down the driveway, grabbing my glove and sprinting to the chip shop, where Grandpa Byron is waiting for me. I walk in trying to pretend that nothing has happened, and hoping that Grandpa Byron won’t notice anything. I mean – what is there to notice? I look fine.

“Oh my jolly goodness – what on earth is the matter?”

All right. So much for that theory. Grandpa Byron’s staring at me. He looks at his watch. “You were nearly twenty minutes,” he says. “Trouble finding it?”

I blink, then hold up the glove. “Uh huh. But I got it.”

Wow, I’m thinking. Twenty minutes!

For me, it’s been several hours, but Grandpa Byron has only been here twenty minutes. Except … those hours must still have happened. Those hours happened to me, so they must have happened to Grandpa Byron.

But when?

That’s the question I simply cannot answer. How could something happen, yet not happen?

All of this is going through my head while Grandpa Byron keeps asking me questions. “Where have you been? I was about to come lookin’ for you, man. Are you a’reet? You look terrible. What happened?”

There’s a big mirror down one wall of the chip shop and I look at my reflection. Well, honestly – I don’t look that bad. A bit dishevelled, maybe, and my hands are filthy, and there are a few smudges of dirt and sand on my face from brawling with Pye, and my feet are wet from where a wave caught me and … yeah, OK, I look a bit messed up.

“I, er … I couldn’t find it, and then I was running back, and I tripped up …”

“What aboot yer feet? They’re soakin’, man!”

“Puddle? I, er, stepped in a puddle.” If Grandpa Byron realises the absurdity of this – it’s a sunny, dry day with no puddles – he isn’t showing it. He stares at me, really carefully, as he slowly eats a chip. Then he makes a face.

“Yuck. They’re cold. Ha’way – let’s go.”

I’d love love love to tell Grandpa Byron that I’ve just met Dad. But I can’t. The frustration keeps me quiet and I can’t talk on the back of his scooter anyway. And besides, one thought is crowding everything else out: I must save the time machine from discovery when Bella and Graham’s builders get to work. That could be as early as tomorrow.

One way or another, I’m going to be back in Culvercot tonight.