At the end of the week there had been another lesson, and at the start of the following week another one again. Sometimes they could sneak a lesson in before Nancy’s duties began at dawn, and sometimes – on Sundays, when the ballroom was closed – they could meet in the studio behind the ballroom after dark, while the rest of the hotel buzzed on around them. Soon, Nancy got to look forward to the hours she would snatch with her dancing partner.

He’s never less than a gentleman, she wrote to Frank one night. And do you know? I think I can do it. Mr de Guise has made me see that, just because my body has let me down in the past, it doesn’t mean it has to let me down for ever. It doesn’t mean that I should always be ‘Nancy with the sickly leg’. Mr de Guise says he can hardly see it any more.

‘It’s part of you,’ Raymond said one day when, after a hard morning working the fifth floor with Mrs Moffatt, Nancy moved awkwardly across the dance floor – and, angry at the way her leg put up protest, tore herself out of Raymond’s hold. ‘Don’t fight it all the time. Fighting it doesn’t make it any better. If you have to . . . why, make it a part of the dance.’

Nancy grinned at the absurdity of the idea. ‘I can’t imagine Hélène Marchmont or Sofía LaPegna have ever stumbled around and just pretended it’s part of the dance.’

‘Well,’ joked Raymond, ‘maybe that’s because they don’t have the imagination.’

And after that, Nancy wrote later that night, I hardly think about it at all. Sometimes I’m not as elegant as I might be. Sometimes my leg takes a moment to realise what the rest of our bodies are doing. I used to think about it so much I’d be willing it to happen, Frank. But now? Now we just glide along . . .

They were gliding along one Sunday evening when the studio door opened and in strode Hélène Marchmont, tall and striking in her coat of sable fur and a red cloche cap. Nancy, who had been learning the rudiments of the tango, felt suddenly exposed. Her legs seemed to dance on, but her body turned around – and only by steadying herself against Raymond’s body did she stay upright.

Her cheeks flushed crimson.

‘Hélène,’ Raymond began, and rushed to meet her at the door. Nancy watched as they whispered together. Once, Hélène looked up, over Raymond’s shoulder, and her eyes seemed to take the whole of Nancy in. I’d never felt so small, she wrote to Frank. The Empress of the Ballroom, Hélène Marchmont – and there was me, little Nancy Nettleton. I was having to concentrate just to stay on two feet . . .