All of that happened last summer.

All through the winter, and into the spring, I would look at Mum’s tree bent over the skyline, and I would feel that something wasn’t right.

Something was left unfinished. And today I’m going to finish it.

Dr. Pretorius’s disk cassette is still disguised as a Famous Five book. I have wrapped it in plastic, and sealed it with packing tape, and put it in an old tin and melted candle wax around the rim of the lid.

It’s very early on the morning of Dad and Jessica’s wedding and I’m the only one up. Mr. Mash and I walk up to Mum’s tree with a spade, and I dig a deep hole underneath the branches while my dog watches.

It’s the first of May. There’s a clear blue sky, and a light breeze is shaking the boughs, which are heavy with pearly-white cherry blossom. The blossom is due to drop at any time now.

It’s perfect.

I place the tin with the disk in the hole and fill in the soil, stamping on it while Mr. Mash sniffs the ground curiously. I look back at our farmhouse, and across the fields to the silvery strip of sea; then I check around that no one’s listening. I’ve never done this before, but I’ve heard Dad talking to the tree as if it’s really Mum.

“Mum?” I say out loud. “I don’t know if anyone can ever create the dome again, but I’m leaving this here for you to look after. Just in case, you know.”

It feels strange, talking out loud, but Mr. Mash is listening, with his head tilted to one side, and so I carry on.

“I wish I could have saved you, too, but it doesn’t work like that. But we saved other people, so you know…”

I stop for a while.

Then I say, “Were you helping me? I think maybe you were. That’s what mums do, isn’t it?” I’m remembering how I thought of Mum’s song, before deciding to bust Dr. Pretorius out of the hospital, and Other Me didn’t, and how that seemed to be the difference between our timelines.

I pause for a bit and look up through the branches. Finally, I say, “Talking of mums…You’ll always be my real mum, but…I kind of have a new one now. I hope that’s OK. Shall we call it the Big Experiment?”

That’s it. I sigh deeply and contentedly and prop the spade over my shoulder. “Come on, Mashie,” I say, and start to head back down the path. Mum’s song—the one from Chitty Chitty Bang Bang—is playing in my head and, at that moment, the breeze picks up, and a blossom petal floats past me. Then another, and another, till Mr. Mash and I are enveloped in a cloud of white as a strong gust shakes all the blossoms from Mum’s tree, casting them onto the path before me.

Mashie’s jumping up, trying to eat the petals, and I know then that everything’s going to be all right.