I squeezed through the gap and he slammed the door shut and bolted it. We stood face to face inside the dark hallway in silence. I was about to speak but he put a hand on my arm to caution me to be silent. At once I froze. Outside I could hear the normal noises of the London street, people walking by, a few tradesmen calling out, street sellers offering their wares, the distant shout from someone unloading at the river.

‘Did anyone follow you? Did you tell anyone you were looking for me?’

My heart thudded at the question. I felt my hand go to my cheek as if to rub off a smut. ‘Why? What has happened?’

‘Could anyone have followed you?’

I tried to think, but I was aware only of the thudding of my frightened heart. ‘No, sir. I don’t think so.’

John Dee nodded, and then he turned and went upstairs without a word to me. I hesitated, and then I followed him. For a groat I would have slipped out of the back door and run to my father’s house and never seen him again.

At the top of the stairs the door was open and he beckoned me into his room. At the window was his desk with a beautiful strange brass instrument in pride of place. To the side was a big scrubbed oak table, spread with his papers, rulers, pencils, pens, ink pots and scrolls of paper covered with minute writing and many numbers.

I could not satisfy my curiosity until I knew that I was safe. ‘Are you a wanted man, Mr Dee? Should I go?’

He smiled and shook his head. ‘I’m over-cautious,’ he said frankly. ‘My father was taken up for questioning but he is a known member of a reading group—Protestant thinkers. No-one has anything against me. I was just startled when I saw you.’

‘You are sure?’ I pressed him.

He gave a little laugh. ‘Hannah, you are like a young doe on the edge of flight. Be calm. You are safe here.’

I steadied myself and started to look around. He saw my gaze go back to the instrument at the window.

‘What d’you think that is?’ he asked.

I shook my head. It was a beautiful thing, not an instrument I could recognise. It was made in brass, a ball as big as a pigeon’s egg in the centre on a stalk, around it a brass ring cunningly supported by two other stalks which meant it could swing and move, a ball sliding around on it. Outside there was another ring and another ball, outside that, another. They were a series of rings and balls and the furthest from the centre was the smallest.

‘This,’ he said softly, ‘is a model of the world. This is how the creator, the great master carpenter of the heavens, made the world and then set it in motion. This holds the secret of how God’s mind works.’ He leaned forward and gently touched the first ring. As if by magic they all started to move slowly, each going at its own pace, each following its own orbit, sometimes passing, sometimes overtaking each other. Only the little gold egg in the centre did not move, everything else swung around it.