Since those days when they had listened to each other’s stomachs rumble in Butler’s Buildings, Sal had become a different creature…her face had a beaten look now, her cheeks sallow. Her voice was squeezed of all its laughter. In this Sal he could recognise nothing of the other Sal, her face soft in the candlelight at the table, the pucker between her eyebrows as she dotted out the letters for him to trace. At times, the sudden thought of that Sal pierced him like a light shining out in a dark night.

It was plausible that a nine-month voyage into exile would change a woman. But the change had all happened off-stage, between pages 74 and 75. That made for a very bumpy and unsatisfying experience for the reader.

That was straightforward enough, and I was scribbling notes as he talked. Change too abrupt. Show change. Smooth transition. I was still thinking of it as a technical problem.

But then Michael said, ‘in the London scenes you’ve got an opportunity to complicate her later grumpiness’ and I saw that this was an invitation to walk into the book and look around— not as a plumber come to fix the pipes, but as an architect seeing what else you might do with the space.

We turned through the pages together, and it was as if Michael’s comments were a map of the book I’d written: not suggestions, but a sketch of what was there: ‘Sal dislocated, cannot recognise home. Sal tough about Scabby Bill. Sal diminished.’ The architect was being given a plan of the place, with the windows drawn in and the height of the ceiling given.

He used the word ‘darken’ to suggest what might be done to Sal’s character in London. The word worked like the opening of a door: I could see the space beyond it, and suddenly couldn’t wait to enter it, see what was there, do things with it.

What an astonishing thing memory is. It must have been over forty years since I’d read Black Beauty by Anna Sewell—up in that treehouse, a piece of forbidden chocolate probably melting in my fingers, a glass of milk threatening to tip over as the branches heaved in the wind. I’d never thought about it since. Kids didn’t seem to read Black Beauty these days.

But feed the idea of ‘darkening Sal’ into the mysterious machinery of the unconscious, and out came that scene in Black Beauty where a man whips a horse that’s fallen down in the street.