So it’s half-past midnight and I’m in a taxi going to Culvercot. In my hand is a carrier bag containing Alan Shearer, the hamster. Well, he’s in a little stiff cardboard box that Steve’s smartphone came in, with holes punched in the ends with a pencil so that he can breathe.

He’s going to go in the time machine first. My hamster, as it were, will be my guinea pig.

Grandpa Byron’s moped is still chained to the drainpipe and he has not yet got round to hanging a spare key to the padlock on the kitchen hook, as I discovered after school when I came up with the new plan. Besides, I was feeling pretty nervous about risking a second moped ride. What if the same cops were on duty?

In my moneybox there was eight pounds in change I’d been saving – plus the forty I got from Grandpa Byron for my birthday.

My mobile phone is supposed to be strictly for emergencies only. This, I figure, counts as an emergency, so I went online and booked a cab from a taxi company in Ashington, which is the next small town up the coast, as I didn’t want to use the local company. I arranged a pick-up at the corner of our street, and I felt my stomach flutter when I saw the yellow light approaching and I stepped out from the shadows to flag it down. The driver’s window came down and he looked me up and down.

“You book a taxi, son?”

“Yeah,” I said as casually as I could and reached for the rear-door handle.

“Ha’d on, ha’d on,” he said and I heard the thunk of the central locking system. “You’re a bit young to be tekkin’ cabs in the middle of the night, aren’t ya?”

I was ready for this. Carly and I had gone over just about every query and hitch we could think of.

“I’m fifteen,” I lied. “And besides, my money’s as good as anyone else’s. And there’s a tip.” I held up a twenty-pound note. The quoted fare had only been fifteen pounds. Greed got the better of him.

“Gan on, then. Gerrin quick,” he said. The door unlocked.

The next bit we’d got planned too. I dial Carly’s mobile number from inside the cab and she picks it up straight away. I hold my phone so that the driver can hear Carly’s voice.

“Hi, Mum, it’s me, Freddie … yeah, I’m in the cab now … no, don’t, I’ll let myself in by the garage … yeah … uh-huh … only an hour? … well, if you say so, Mum … I’ll ask if he can take me back.”

And this is where I speak to the driver, who has been watching me in the rear-view mirror. “Can you take me back in an hour? I’m going to my dad’s but my mum wants me home soon.”

Now, I’m figuring that two easy twenty-pound fares an hour apart is worth more to him than pootling around trying to pick up little fares in Culvercot past midnight, and that he’ll wait. It’s a gamble, though, and I haven’t really worked out what to do if he says no.

“I’ll wait for ’alf an hour but norran hour,” he says.

“He says half an hour, Mum,” I say to Carly, and then to the driver, “She says OK.”

He gives me another long look in the mirror, but says nothing. And even if he had, I was prepared with a story about my mum and dad being separated and my dad living with Aunty Ellie and this being the only time I could visit him, or … something. To be honest, Carly and I didn’t quite put the finishing touches to this story, which we were hoping – correctly as it turned out – we wouldn’t have to use.

Twenty minutes later, we’re outside 40 Chesterton Road. I’ve handed over the money as we turn into the street, as I want to be out quickly. I thought about asking him to drop me at the end of the street, but it seemed suspicious, and besides – a cab driver with a passenger my age is going to make sure the kid gets safely indoors.

So here I am: the taxi is in the middle of the road, with its engine idling as I nip up the driveway towards the garage doors. The taxi door had shut with a louder noise than I had hoped, and just as I’m squeezing through the gap in the garage doors, it happens: the light goes on in the front bedroom and my stomach lurches.

By poking my head round the gap in the doors, I can see the taxi, and the curtains parting in the bay window above.

It gets worse. The taxi driver gives a wave to whoever is peering through the curtains, points at the garage and gives a thumbs-up. It’s easy to guess what he means: “I’ve delivered your son safely, and he’s comin’ in now.”

The taxi pulls away to the parking spot down the road where he said he’d meet me in half an hour. The light’s still on upstairs and the curtain flicks open in the side bay window as the lady looks to where the taxi driver was pointing. As the shaft of light hits the garage door, I pull my head back. Has she seen me? Will she notice that the garage door is ajar?

So I’m waiting until I get the courage to move again when I hear the key in the lock of the door that connects the garage to the house. The door bursts open, the garage light goes on and whoever opened it sees … nothing. For by this stage, I’ve snuck back out of the garage, and I’m crouching down between the Skoda and the hedge. If they decide to look outside I’m done for.

A woman’s voice comes from inside the house.

“You’ve got to sort that garage door out, Graham!”

“Yeah, yeah, yeah,” and Graham pulls the door shut again.

I hear the key in the connecting door and a minute later the light upstairs goes out. I decide to wait at least ten minutes before going in again, so now I’m going to have to work double quick.

It’s amazing what you can do under pressure, when you don’t have time to dither.

I’m quick and I’m quiet, getting into the old cellar – under the old planks, through the circular metal submarine door, down the stairs, and I’m sitting at the desk, looking at the wall and taking deep breaths, trying to stop my heart from racing, but I can’t – it’s just going thumpa-thumpa-thumpa in my chest. I’ve still got Alan Shearer in the box inside the bag, and I take him out and let him have a little run around on the desk: he seems fine.

So there’s the tin tub with the old MacBook laptop computer in it. There’s a cable coming out of the back of the laptop leading to a black metal box about the size of a book, and coming out of that are two cords with the strange hand grips – more like huge metal bolts, really – on the end.

There is a metal clasp on the side of the black box and I flip it open and lift the lid. Inside is a circuit board like I once had in a home electronics kit and two tiny gold-coloured rectangles. A long cable is attached to the circuit board and at the end of the cable is a bare wire with a blob of Blu-tack attached to it.

It all looks as though a six-year-old has made it.

My hands are trembling as I plug in the laptop to a wall socket and there’s a slight hum and a delay of a minute or two as it runs through its start-up programs, and then the screen comes to life, and the desktop picture appears of Dr Who and his Tardis, only not the guy who’s Dr Who at the moment but the one from a few years ago whose name I can’t remember because I’ve never really been into Dr Who.

And there’s one folder on the screen desktop, just the one, a little blue square labelled ‘Al’. With my hand on the touchpad I click on the folder. There are two sub folders inside: one labelled ‘map’, and another labelled ‘Al’. I click on the ‘map’ one first: it’s like a simplified version of Google Earth with a grid laid over it and a box for entering map coordinates. There’s a look about it that says “don’t mess”.

So I quickly close it before I can hit anything accidentally and open up the one marked ‘Al’ instead. There is a single document inside it, and a dialogue box appears, asking me for a password, with the question:

Name a well-known homemade go-kart

I smile and type in The Lean Mean Green Machine, and the document opens.