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was very modestly constructed with walls of oak and wattle, though at some point in its history a thatch roof had been replaced by one of lead.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.’