‘Once upon a time, there was a sad, lonely little girl called Beatrice.’

The twins were far too young to understand the story, of course, but they stared solemnly at the pictures as they rose up out of the pages. Rosa had learned that, of the two of them, Esme had the gentler nature, and cuddling often seemed to quieten her. Ada was usually much more difficult to please, but even she appeared to be interested in the book, so Rosa kept on reading.

‘One night she was feeling especially alone because an angel had taken her mother. But then the ice clock chimed, the white frog appeared on her pillow and ice roses filled her bedroom …’

Rosa often returned to the book when the twins were hard to settle. Ada, in particular, would sometimes cry disconsolately for hours in the evening, and there seemed to be nothing that Rosa could do or say that would soothe her – except to read from the Winter Garden book. Ada’s red, outraged face would soften and her tears would dry up, as the pages seemed to emit faint scents of candied fruit and frosted pine.

Then one night something extraordinary happened. Rosa had finished the story, the twins were both asleep at the same time for once, and Rosa was keen to crawl into her own bed for an hour or two before one of them inevitably woke. But when she tried to turn off the carousel’s music, the mechanism got stuck. The key refused to move and the lullaby continued to play.

And then, one by one, the tiny ponies left the carousel. Rosa stared. She had not designed them to do that, but she knew from experience that sometimes her clockwork creatures could take on a life of their own. It usually happened when they had existed out in the world for a little while and had begun to develop their own souls.

They stepped off the carousel’s platform straight onto the window ledge. One of the ponies kicked the frame beyond the bars and the window swung open – only a few inches, but it was enough for the ponies to tumble out onto the ledge.

Rosa lurched after them with a little cry of dismay, but before she could stop them, they’d leapt from the edge, to be swallowed up by the deep snow in the grounds below. She quickly closed the window. Esme had been looking a little sickly the past few days, and the last thing she needed was icy air blowing into the room.