Next morning, Gram is as nice as pie, all smiley and morning-brisk. As if nothing at all is going on.

I almost convince myself that I’m imagining all the odd stuff over the last few days and weeks, and the rummaging sounds coming from her room the night before.

I’m still off school ‘sick’, you’ll remember, but I’m downstairs in my school uniform as usual.

Gram leaves before me, and I’m left to lock the house and take Lady to the dog-sitter. (It occurs to me that I could save the £10 that we pay the dog-sitter and keep it, and I’m on the verge of doing just that when my conscience speaks up and reminds me that I’m already involved in a web of deception. I don’t really need to add to it. Besides, I’d just get found out.)

So I drop Lady off at the normal time, but instead of carrying on to school, I double back and I’m home again before school has even started, standing in the middle of Gram’s bedroom and staring at the top cupboards.

Gram’s room is by far the neatest and tidiest in the house, probably because I never go in there. Everything is put away: there are no blouses slung over the back of a chair, no stray socks, or books on the floor. The top of her dressing table is home to a silver-backed hairbrush and a carved box with a lid, full of loose change. Everything is blue or grey. The carpet is grey, the bedcover is blue stripes, the cushions are blue and white, the curtains are grey and white and blue. It smells nice, like Gram’s perfume and deodorant.

There are built-in wardrobes along one wall, with a row of cupboards along the top going up as high as the ceiling.

I grab the little stepladder from the cupboard. There are only three steps on it. Even on the top step, I have to strain to see into the first cupboard I open. It contains pretty much what I expect to find: blankets, a spare duvet and a long Puffa jacket that Gram bought, wore once, and then saw someone on TV wearing one similar and never wore it again.

The second cupboard is empty. The third has more sheets, and a cardboard box containing my old picture books from when I was little, and I spend a happy half-hour looking through them and remembering how Gram used to read them to me. (Gram said she was going to give them to the church book sale, but that was ages ago so I suppose she has just forgotten.)

The last cupboard is just cupboard junk. There’s an old sewing machine that never gets used, a bag of old clothes and a pretty brass vase thing with carving on it.

That’s it.

Can Gram really have been taking down the box of old picture books to look at? I hardly think so.

Frustrated, I’m up on the steps again, putting the book box back, and it’s not an easy task when you’re as small as I am. As I lift it up, it tips back and a few books slither out and land on the floor, so I have to come down the steps and put the box down to retrieve them.

One has skidded across the carpet and under Gram’s bed, and I’m on my knees to get it.

That’s when I see it.

A metal box. I know it’s what I have been looking for. Don’t ask me how I know. I don’t even know myself. But I just know.

Gram must have taken it down from one of the cupboards and put it under the bed – why, I don’t know. Maybe so she can access it more easily?

I reach under and pull it out. It’s quite big: the top is about the size of a tea tray, and it’s about six centimetres deep.

And it’s locked. Of course it is. It had to be.

There’s a padlock with a combination lock securing the lid to the box with a little latch, and my heart sinks. If it was a key lock, I could at least look for the key, but it’s not.

Can I guess the code? It’s four digits.

I try some obvious ones: the year of my birth, the year of Gram’s birth, then each year either side in case I got it wrong. The last four digits of her mobile number. The first four digits of her mobile number, then mine.

Then 1066 because of the Battle of Hastings, and 1815 because of the Battle of Waterloo, and 1776 because we’ve just done the American War of Independence at school.

It’s hopeless. I’m never going to just guess.

But …

I could try every number from 0000 to 9999.

Every single one.

How long will that take? I do a quick calculation on my phone’s calculator. Assuming two seconds to input each new number (might be quicker?), and rounding 9,999 up to 10,000, that’s 20,000 seconds. Divide that by sixty to find out how many minutes … that’s 333 (point three recurring, actually) and divide that by sixty to get the hours and I’m looking at …

Five and a half hours.

On Tuesdays, Gram’s back by lunchtime.

I’ll just have to hope she hasn’t chosen a high combination number.

I get to work immediately.

0000

0001

0002

0003

0004

After each turn of the dial, I give a little tug to see if it has worked. I can’t be slapdash – I don’t want to get to 9999 and realise that I have missed one, or failed to test the lock on each number.

So here I am, sitting on Gram’s bedroom floor, with my back against her bed and the metal box in my lap, turning the combination dials and tugging, again. And again. And again …

An hour goes past.

2334 tug

2335 tug

2336 tug

I get up and stretch and go to the loo and make a cup of tea.

Another hour.

3220 tug

3221 tug

My shoulders are aching and my fingers are hurting from the sharp edges of the number cogs.

Another hour.

I’m looking at the clock nervously as it ticks towards midday. I’m thinking to myself, So long as Gram doesn’t come home early, I’ll be OK.

No sooner do I think that than I hear her car outside.