Today was the first day of filming. Not a lighting or camera test, but the real thing. Tonight, there would exist a length of exposed film showing me – or at least someone who looked a bit like me – acting in her very first moving picture. The nerves I had endured last night were gradually replaced by relief that we were getting on with it at last. And as the day went on, the pieces of the kaleidoscope that had so baffled me began to settle.

We did the scene we had rehearsed yesterday. The set and lights were checked, Aidan and I “blocked” the scene, making our moves without acting or speaking, and the lights were adjusted until Harry, behind the camera, was satisfied. Then he shouted, “Set!” which meant, “Everyone on the set who shouldn’t be, clear off!”

David, who was such an exacting director that it had taken ages to get the scene set up to his liking, eventually called “Roll camera!” and Harry started the camera and called back, “Rolling!” Then Dennis called for the clapperboard.

The contraption known as the clapperboard seemed to me old-fashioned. The primitive wooden board with a hinged top seemed to have no place in this modern, electrified studio. It did not take me long, however, to realize it was the most important piece of equipment of all. Without it, it would be impossible to make a film.

The clapper boy, as he was called (though he was not a boy at all, but a man called Bernard who was at least forty), was the clapperboard’s master. As soon as the camera started rolling, he put the board in front of the lens and “clapped” the hinged part down to signify that the scene was being filmed. Only then did David call “Action!” and the filming properly began. After each scene, Bernard bore the clapperboard away with a proprietary action, rubbed off the scene number, and chalked on the next with a piece of chalk he wore on a thin chain around his neck. Sometimes he would have to wait a long time before he could do this, but it was his job and no one else’s. Ever.

I was thrilled that at last I understood. When Frank threw his leg over his bicycle or tossed a bale of hay onto the stack or clattered down the stairs in his nailed boots, he would shout, “Lights, camera, action!” Now, I could tell him exactly how those three elements combined to film the scene. My next letter to him would be a long one.

As I set this down all these months later, it seems as banal and repetitive as Aidan considered the business of making a film. But then it was the most exciting thing imaginable. That moment when the clapperboard went “smack!” and I put my actress’s face on was like an alarm clock going off. “Get up, Clara Hope,” it said, “and do what – astonishingly – you get paid to do!”

Furthermore, to my inexpressible relief, Harry’s call of “Rolling!” seemed to work magic on Aidan. He kept his head down while Bernard slapped the clapperboard shut. But then his head came up, and a miracle took place.

He began to act.

There was a light in his face that had not been there in rehearsals; a quickness, as if his internal battery had been switched on. Not only did he not improvise or giggle, he played the part with such professionalism that I forgot he was Aidan and started to believe he was de Montford. It was suddenly much easier to be Eloise.

“Marvellous! Perfect!” exclaimed David when the take was over. He came towards me, applauding, his face pink with excitement. “Clara!” His voice was almost a shriek. “That was absolutely wonderful. You’re a natural, just like I said.” I was sitting down; he put his hand on my shoulder in a fatherly way. “Now, why did you not show us this in rehearsal? I’ve been worried sick that you wouldn’t do!”

“So have I,” I confessed. “But … I don’t know, it just felt so different to know it’s a real performance that people are actually going to see.”

I did not add that the sudden attention that Aidan had brought to his own performance had given mine life. David squeezed my shoulder. “We’re going to do another take, and we don’t know yet which we’ll use, so you’ve got to give it everything this time as well, all right?”

I nodded, happy in the expectation that Aidan would also “give it everything”. It was his ability to do this, I realized, that must show in screen tests and get him parts. “Natural” or not, I must seem to Aidan Tobias an amateur who had got the role by means of mere luck. In contrast, he was an actor of rare ability, much more deserving of praise than I. Yet David had pointedly, publicly ignored him.