My 8-year-old son gave up his lunch money to buy a little girl with Down syndrome a red dress—the next morning, our lawn was covered with lunchboxes, but what was inside the biggest one made him go pale.

That is a whole story on its own and it is the one everybody wants, and it is not the reason I am writing this.

Because there was one more.

In the middle of the lawn, on its own, with a clear gap around it — somebody had deliberately left a space — there was a lunchbox that did not belong with the others.

It was metal. Battered. Dark green with the paint gone through to bare steel on the corners, the old rectangular kind with a domed lid, the sort men took down a mine or into a plant in 1970.

It was enormous next to the plastic ones.

And there was a piece of paper taped to the lid, in biro, in capitals:

OPEN THIS ONE FIRST.

Felix went and knelt down in front of it in his pyjamas.

He undid the catches — they’re stiff, you have to push both at once, and it took him a couple of goes — and he lifted the lid.