It wasn't the first time Belisarius had seen such behaviour among the Germans. Masters commonly copulated with their slave girls in the open, even when they were trying to sell them in the markets of Brycgstow. But as Macson murmured, 'This is not an approved monkish custom, I don't think. But I wouldn't be surprised if this village is full of little tonsured bastards.'

At last, with a shudder of his white thighs, the monk spent himself and rolled off. The girl lay for a moment, her legs splayed, her tunic stained with his sweat. Then she stood, straightened her clothes, and immediately trudged off to the fields.

Macson stepped forward. 'You must be deacon Elfgar.'

The monk opened his eyes, startled. He jumped up, pulling his habit down over his limp cock. 'God be with you,' he murmured in Latin, sweating.

Boniface had a novice called Aelfric serve Belisarius and Macson a little wine. It was at the express permission of the abbot; otherwise the brothers only took wine with their noon meal, the prandium, on Sundays.

'We live according to the guidance of Saint Benedict,' said Dom Boniface in his heavily accented Latin. 'The rules are elaborate, but at their heart are simple principles. Our waking hours are devoted to the Work of God, the Work of the Body, and the Work of the Mind.' Opus Dei, Opus Manuum, Lectio Divina. 'And as far as possible we inhabit the Great Silence, listening only to the echo of our own souls, and the Thoughts of God…'

They sat in the monastery's small library, a nest of books, scrolls and bound parchments heaped up on shelving. The only light came from oil lamps. There was a smell of old leather and sour ink – although that was to be preferred to the seven varieties of shit that greeted the nose in the average German village.

The only other person in the room was this young novice who served the wine, Aelfric, a slight, oval-faced youth. Macson could hardly keep his eyes off Aelfric's smooth neck – but he was obviously confused by his own reaction. Belisarius understood what was going on, but decided mischievously he would let Macson suffer a little before putting him out of his misery.

And Aelfric, though the novice scarcely said two words, seemed fascinated in turn by Belisarius, a man of the Roman east. The Greek recognised a deep curiosity in her.

Deacon Elfgar had brought them to the monastery in the middle of the afternoon. They had been welcomed by the abbot, who promised to look over Belisarius's stock of books for sale – but not until the end of the monastery's day. While Macson retired to a cell and slept, the death of his father still weighing on him, Belisarius had explored the monastery, with its little workshops and gardens tended by silent monks and novices. He sat in on no less than three services in the little church, intoned and sung beautifully by black-robed monks lined up like so many crows.

Theirs was a rigid, enclosed life, with every waking hour dedicated to some purposeful task or other, with little room for the exercise of free will. But, compared to the chaos outside, this was a calm, ordered, thoroughly civilised environment, and it was no wonder that the sons of kings fled here. Why, the monks even had a latrine that sluiced into running water.

The church, dedicated to Saint Peter, was very modestly constructed with walls of oak and wattle, though at some point in its history a thatch roof had been replaced by one of lead. Rather gruesomely the coffin containing the remains of the monastery's greatest saint, Cuthbert, sat in the middle of the floor. But this wooden cathedral was crammed with treasures: an altar service of gold and silver, some quite exquisite stained-glass panels, and frescoes and vestments adorned with intriguing tangled designs, woven with glittering gold. Even Cuthbert's coffin sat in a jewel-crusted shrine. Belisarius was astounded by the wealth he had found in this remote and rather shabby place. It augured well for his book sales, he thought.

And all of this in a monastery where not a hundred paces away people lived in a house built around a sacred tree.

After cena, supper, which the monks shared with their guests, and the last service of the day, compline, Dom Boniface had at last guided Belisarius and Macson to the library. It was a small collection, dwarfed, said Boniface, by a much greater amassing at the monastery of Saint Paul on the mainland, where the famous Bede had once worked. But still there were volumes here to be proud of – and Belisarius's professional eye quickly spotted a few gaps his own stock would fill.

And here, Boniface promised, inscribed on cool vellum, were the enigmatic stanzas of the prophecy Macson had come so far to see.

Boniface was a 'computistor'. His primary function was to calculate the date of Easter and other significant calendar days for his fellow monks. He was disfigured by a swollen, red-purple tumour on his cheek. Belisarius had been unable to resist remarking gently on the contrast with his monastery name, Boniface. The monk smiled, and called it 'God's joke on a sinner'.

As Belisarius listened absently, the old computistor spoke of the challenges of his life. 'It's a continual battle, to keep faith burning bright in the souls of the people,' he sighed. 'It gets harder every time there's a joint in time – like the midsummer festival they will soon be celebrating – for joints in time, like joints in space at river banks or crossroads, are holy for these people. And every time there's a plague, out come the straw dolls to be tied to the branches of their sacred trees.'

Belisarius nodded. 'It seems to me that Christianity needs to be primitive here. I don't mean that unkindly. You must combat the magic of paganism with the greater magic of Christ.'

'Oh, yes, there's no doubt about it,' the computistor said, his tumour flaring hotly. 'Not only that, we must colonise the pagans' emblems of belief. Think of Christ nailed to His cross. He is pinned to a tree, the fount of wisdom for our German forefathers, and fixed with iron nails, like the elf-shot which brings the pagans sickness and death. What a rich mixture of symbols, eh, Belisarius?…'

They talked on. And at last, with ill-concealed impatience, Macson brought the conversation around to the subject of the Menologium of Isolde.

Truth be told, this 'Menologium', as Boniface called it, was only a curiosity for Belisarius; he had let it guide his footsteps here but he expected little of it. But now he had a chance to inspect it he grew intrigued. It was written in some sort of German, competently transcribed, rather crudely illuminated. He counted a prologue, nine stanzas and an epilogue, all more or less puzzling. The poetry seemed authentically German, what he knew of that earthy art form, with each line composed of two balanced halves, each with two stressed syllables. It was peculiarly full of numbers for a product of a more or less innumerate people.

'It is enigmatic,' Boniface said, watching Belisarius's reaction. 'But as a prophecy it is true.'

'How do you know?'

And Boniface summarised the first four stanzas, explaining the meaning of each of them, leading to the summoning of Cuthbert by the King in the year 684 by the Christian calendar.

Macson sat up straighter, his greed evident in his posture.

Belisarius asked, 'Are prophecies possible in your theology, Domnus?'

Boniface said, 'Ah! Interesting question. Can even God know the future? Augustine of Hippo believed that God stands outside time, and sees past and future all of a piece – as a scholar might survey the pages of a book, laid out on a table before him. But even Augustine put limits on God; he didn't believe God could change the past, for instance.'