There was, though, one picture which showed one star looping on an egg-shaped course around another. This was the diagram which Aethelmaer had unpicked to establish that the comet that had marked Aethelred’s birth was destined to return in the year 1066.

Sihtric asked, ‘And who taught the boy to draw these designs?’

‘Nobody,’ breathed Aethelmaer, and his eyes gleamed, for this was evidently the mystery that informed his whole life. ‘Nobody. He was drawing such designs from the age of four, almost as well-executed as these from the very beginning, his limits only his childish hand, his inexperience with the pen. Somehow all this was poured into his head.’

‘From where? How?’

Aethelmaer shrugged, and winced with pain. ‘How can I know? From God, perhaps.’

Godgifu murmured to Sihtric, ‘That sounds like the origin of the Menologium of Isolde.’

‘Yes. Then perhaps this prophecy, if that is what it is, and the Menologium, have a common source.’

Aethelmaer said, ‘You understand this was all before my time. I was born in the year Cnut came to the throne - long after poor Aethelred had gone back to his Maker. But as a young deacon I showed aptitude for study, and the abbot set me to working on the papers Aethelred had left behind.’

‘And what happened to you?’ Orm asked bluntly. ‘Were you born like this?’

‘Oh, no,’ Aethelmaer said, and he squirmed as the young monk worked at his legs. ‘When I was young I was strong and fit. But I became obsessed with Aethelred’s works - and I let my obsession carry me too far ...’

He had become convinced that he had to try to build some of Aethelred’s marvellous designs if he were to understand them fully. But there was much depicted in the diagrams he could not buy or make: very fine cogs, for instance, with accurately spaced teeth. ‘Perhaps the Romans could have made these things - or perhaps the men of some future empire will be able to do so - but not the monks of Cnut’s England ...’ However he had attempted one of the simpler-looking devices. He showed Sihtric a drawing of it. It was a kind of suit, of wood, cloth and feathers, shaped like a bird, which a man would wear.

‘I can guess what its function was,’ Sihtric said dryly. ‘And I can guess what happened to you.’

‘I hoped to fly like Daedalus!’ sighed Aethelmaer. ‘I fixed the wings to my hands and my feet. I jumped off a tower. I crashed to the earth ... But I flew,’ he said, and he smiled as he remembered his life’s defining moment. ‘And not many men can say that, can they?’

‘No indeed,’ said Sihtric. ‘And Aethelred? You said he was dead before you were born.’

‘Ah. Now that was a sad story ...’