Such freedom ended, of course, in the atrocities that followed, in the years of bloodshed we now call the Heresy War. Keeler was present on the ground at the start of it. She was a witness to the first acts of bloodshed. She stood in time at the zero point where history turned a corner, and she did so with a picter in her hand, capturing that transformation.

Her story did not end there. She so easily might have been one of the trillions extinguished in the fires that followed. Her name is not commonly known today… except that it is, as Saint Euphrati. She was blessed with divine grace and gifts, and from her – and those few close to her in those bleak years – the essence of the Imperial Creed was born. She was one of the first saints. From her, and those disciples around her, arose the tenets of the Lectitio Divinitatus, the truth of us all, that the Emperor of Mankind is not a man, but a god. It is through her that the truth was recognised. It was in her that our faith was born.

The man with the optics was called Sejan Karyl. We returned to the main halls and sat together, talking of what we had seen.

‘The pict itself isn’t the prize, you know?’ he said.

‘It is beyond value,’ I said. ‘An image of Lupercal, in life, before he fell. The beauty and strength of his visage speak to the depth of the catastrophe that occurred.’

‘Some might say that none should look upon it, ever,’ he said.

‘Who might say that?’

‘The Inquisition,’ he replied, ‘of which, I hear, you are a part.’

‘I believe it should be seen,’ I said. ‘As a warning – to show how even the greatest perfection can be blackened… To refresh our determination to guard against the dark.’

He shrugged.

‘If,’ he said, ‘it is Horus before he fell.’

‘You think it after?’

‘Would that not be a stranger lesson? If that was his face after Chaos stole him? Chaos hides its nature well.’

‘You say it’s not the prize,’ I said, changing the subject.

‘According to the catalogue,’ he said, ‘it comes with notes. Some frail documents written in her hand, describing the image and the circumstances of its capture.’

‘You’ve seen them?’

Karyl shook his head.

‘They are reserved for the successful buyer alone. But I have heard of their contents.’