Just across the road from the house where we used to live before Dad died (the first time) is an alleyway that leads to the next street with a patch of grass with some bushes and straggly trees growing on it. I called it ‘the jungle’ when I was little, because in my mind that was what it was like, but looking at it now I can see that it’s just a plot of land for a house that hasn’t been built yet.

And that’s where I am, still in my full-face motorbike helmet, sitting hidden in a bush in the dead of night, waiting to break into my old house.

There’s an old fried-chicken box that someone’s thrown there and I can smell something foul and sour, which I think might be fox’s poo. The house is dark; there are no lights on. I’m looking up at my old bedroom window, the small one over the front door.

By day, Chesterton Road is pretty quiet – a long curve of small, semi-detached houses made of reddish bricks. When they were first built, they must all have looked exactly the same, but now people have added fancy gates, garage extensions, even a massive monkey-puzzle tree outside old Mr Frasier’s, so these days they’re all a bit different.

Now, at nearly one a.m., there’s no one about and I’ve seen enough films and TV shows about criminals to know exactly how not to behave, and that’s suspiciously. If you act normally, no one notices you. If I wandered nervously up and down the street waiting for the right time, then someone might spot me going backwards and forwards looking at the houses, and call the police.

On the other hand, if I’m just walking down the street, then that’s all I’m doing, and it’s as good as being invisible.

(Keeping the motorbike helmet on is a gamble, or what Grandpa Byron calls ‘a calculated risk’. If I take it off, someone might notice that I’m nowhere near old enough to be riding a moped; if I keep it on, that looks suspicious – so I’m still in two minds about it. Anyway, it won’t be on for long.)

I’ve worked all this out on the journey here. About a year ago, when we still lived here, the local council turned off every second streetlight in a money-saving experiment, so where I’ve stopped the moped it is really pretty dark.

As casually as I can, I come out of the bushes, take off the helmet and put it in the moped’s top box. I pull my collar up and, without stopping, walk over the road to number 40. There I turn straight up the short driveway and stop in the shadows, well hidden by both the hedge that divides number 40’s front garden from the one next door and the small Skoda that sits in the driveway.

So far, so good: the new owners of our house have not yet got round to fixing the garage doors. In fact, they’re even less secure than they were. There’s a brick in front of them to keep them shut, and when I crouch down and move it out of the way the right-hand door swings open, then bumps against the Skoda. For a dreadful moment I think the gap will be too small to let me in, but I just manage to squeeze through, and there I am, in the garage, which smells of dust and old oil. My torch is flashing round the walls to reveal boxes that they still haven’t unpacked and, in the middle of the floor, the dark wooden planks covering up the cellar entrance.

Here’s another tip if you’re thinking of breaking in anywhere: don’t flash your torch around too much. A flashing light will attract attention, whereas a still light doesn’t. So I put my torch on the ground and start to lift up the greasy planks.

Under the planks there’s a concrete stairway, and once I’ve gone down it I’m standing in a space about a metre square and to my right is a small metal door that’s about half my height with a dusty, steel wheel for opening it like you get on ships. The wheel is secured into place by a stout bolt with a combination lock.

I try to give a little whistle of amazement, a “whew!”, but my lips are so dry with nerves and dust that I can’t. Instead, I set the combination lock to the numbers Dad instructed in his letter – my birthday and month backwards – grab the wheel with both hands and twist it anti-clockwise. There’s a bit of resistance but it gives with a soft grating noise, and as it spins around the door suddenly pops open inwards with a tiny sighing noise of escaping air.

I grab my torch and aim it ahead of me as I go through the little doorway, crouching. There are more steps down and a wall on my right and my hand finds a light switch but I daren’t try it in case it’s a switch for something else, like an alarm or something, or it lights up the garage upstairs, or … I just don’t know, but I’m too nervous to flick the switch so I look at everything through the yellowy-white beam of torchlight.

The steps lead to a room about half the size of our living room at home, but with a lower ceiling. A grown-up could just about stand up.

Along one long wall are four bunk beds, all made up – blankets, pillows, everything. There’s a wall that juts out into the room, and behind it is a toilet and some kind of machinery with pipes and hoses coming out of it. There are rugs on the white concrete floor and a poster on the wall. It’s faded orange and black with a picture of a mum, a dad and two children inside a circle, and the words ‘Protect And Survive’ in big white letters. I’ve seen this poster before when some guy came to talk about peace and nuclear war and stuff in assembly once, and he’d made Dania Biziewski cry because she was scared and he was really embarrassed.

This is what people built years ago when they thought Russia was going to kill us with nuclear bombs.

I turn round and see what’s behind me. The torch beam picks out a long desk with a chair in front of it. On the desk is a tin tub, like you would bath a dog in or something. In it is an old-style Apple Mac laptop, the white one, and a computer mouse. There’s a lead coming out of the back of the computer leading to a black metal box about the size of a paperback book, and coming out of that are two cords that are about a metre long, with strange sort of hand grips on the end.

Next to the tub is a coffee mug printed with a picture of me as a baby and the words ‘I love my daddy’. The inside of the mug is all furred up with ancient mould.

And beside the mug is a copy of the local newspaper, the Whitley Bay Advertiser, folded in half and open at a story headlined ‘Local Man’s Tragic Sudden Death’ above a picture of my dad.

I sit down in the swivel chair and run my hands over the underside of the desk. When I can’t feel anything, I get on my knees and shine the torch upwards, and there it is: an envelope, taped at the back, just as Dad said there would be.

But there’s no time machine. At least, not one that looks how I imagine a time machine might look.

That’s how I end up staring at the tin tub and its contents.

Surely, I’m thinking, Surely that’s not it?

But it is.

And the craziest thing? It works.