I never knew it was there. Every night the secret was just above my head, in the darkness. I had no idea … never in my wildest dreams. Then something struck in the middle of the night that changed everything.

Since we moved house three years ago when I was eight, I didn’t have a clue what was up in the loft. But a mystery that no one had discovered before was just over my bedroom. It was me who eventually found it. It was me who finally worked out the clues, cracked the code and solved the riddle. It was me who uncovered the incredible truth from 100 years ago. It was me who first saw what it all means. You could say it was like double vision. You’ll soon see why.

The question I’m dying to answer now is very simple. Could anyone else work it out and unlock the secret message? Can you? I’ll tell the whole story and you can see for yourself. You might be able to puzzle it out faster than I did – if you can spot the signs. Keep a close lookout for the clues as I tell you the story that stunned my dad, made my mum cry and changed me forever.

I was woken in the middle of the night. A sudden clattering noise filled my room for just a few seconds. I sat up, blinking into total darkness. After a final click and clunk above my ceiling there was only silence … so I flopped back to sleep.

I forgot all about that noise in the night until next morning, when my little brother Ben blurted, ‘Oh by the way, Mum – someone was up in the roof last night. They were walking around in the loft.’

We all stared at Ben as if he was mad, but then it all came back to me. So I said, ‘Yeah, I remember now – something woke me in the night.’

‘In that case, Sam,’ Dad winked, ‘You can come with me to investigate. But be warned … we might find a dead body.’ He paused for dramatic effect before adding with a smile, ‘I set mousetraps up there a few days ago. Do you still want to climb the ladder into that mousey world of creepy cobwebs?’

I’d only been in the loft once, but I loved it up there. It wasn’t scary, just full of dusty clutter, dark shapes and boxes covered with curtains. It had strange smells and little piles of chewed cardboard left by mice. It would be a great place for a den. I followed my dad up the ladder and poked my head into the cold, eerie world above our bedrooms. I had to be careful where I trod, because Dad said I mustn’t poke my foot through to the bathroom.

A mousetrap above my bedroom had snapped shut and the cheese had gone. The mouse that woke me in the night had a lucky escape. I lifted a sheet beside another trap and uncovered a stack of cases. It was there I saw a small, brown leather case that looked very old and unusual.

‘What’s this?’ I asked Dad.

‘That belonged to your great great grandfather. Do you remember my Grandad Peter? He left me that case, which was his father’s. I’ve never looked inside as it’s locked and I don’t have the key. Apparently it’s got stuff about the First World War in it, so I don’t think it will interest you.’

‘Can I bring it down so we can have a look?’ I asked. ‘We’re learning a bit about the war at school.’

He let me carry the little case downstairs where he looked at it carefully.

‘I’m afraid I’ll have to get some tools on this so we can open it up,’ Dad said.

He then went to a drawer and, after a lot of searching, he found an old photograph and put it in my hand. ‘This was the owner of that case. Meet your great great grandad. You’re in for a shock, Sam.’

I stared at the face of a boy standing in a cornfield. He was dressed very smartly in an old-fashioned school uniform with an unusual collar. On the back of the photo there was faded writing in pencil: GH 1911. But it was the boy’s face I couldn’t stop staring at. It was just like I was looking in a mirror. If I hadn’t known otherwise, I would have sworn it was me.