Karl shoves me in the shoulder and sits up.

‘What does it matter to you?’ he asks gruffly. ‘He was my friend, not yours. I’ve got new friends now. I don’t need Walter.’

He gets up and begins climbing down the ladder.

‘See you later, Little Mouse.’

I sit for a long time, legs dangling through the hole, getting colder and colder.

Does this mean I won’t see Walter anymore? How can that be?

Well, Karl, just because you have new friends, doesn’t mean you have to lose your old ones. I’m going to make sure I keep mine. Because friends are precious. Like jewels.

11 February 1934

The grey streets of Leipzig are hidden beneath a deep layer of crystal-white. Delicate ridges line every branch and twig of the cherry tree, transforming it into the sugar-coated world of the Nutcracker and the Mouse-King.

It’s the first day of the school winter holidays and Tomas, thinly dressed for the weather, hops from foot to foot on the doorstep. His lips are tinged blue.

‘Come out with me,’ he says. ‘I hardly see you these days.’ He wrinkles his nose and pushes his glasses up.

‘I’ve a lot more homework now.’ I hold fast to the door frame. His eyes are too big for his thin face and they protrude, like an owl’s. Behind me, the house is warm and Bertha is making zimtsterne cookies; the smell of hot sugar and cinnamon drifts from the kitchen.

‘We could build a snowman in Rosental.’ His breath fans and coils above his head and I think of how Karl has ditched Walter and how I vowed not to do the same with my friends.

‘All right, I’ll come,’ I say, and as he smiles, his eyes crinkle and disappear.

I pull on my boots, coat and a pair of warm gloves. I think of Tomas’s bare hands. There’s always a whiff of mould about him, a faint hum of sweat, grime and misery. But we were once poor, and I mustn’t hold it against him. I pick up a second pair of gloves and a woollen hat.

‘Here, use these.’ I hold them out for him. ‘It doesn’t matter if you don’t give them back.’

He takes them and strokes his fingers across the wool.

‘Thanks, Hetty,’ he mumbles, looking down. He pulls the hat over his ears and then puts on the gloves. ‘Warm as a hot potato now,’ he says, clapping his hands together and giving me a shy smile.

Snowflakes float peacefully from a low granite sky, drifting onto the mounds piled against the railings. We cross Pfaffendorfer Strasse and walk towards the big iron gates at the entrance to the park. On the side of Tomas’s temple is the large, mottled, yellowy-green remnants of a bruise. Like an apple repeatedly dropped to the floor, I wonder if he is all brown and rotten on the inside too.

‘My father lost his job,’ Tomas says as we kick our way through the fresh, untrodden snow.