The roar of conversation in the church suddenly quietened, and Merthin saw that the monks and nuns were seating themselves. The choirmaster, Blind Carlus, came in last. Although he could not see, he walked without assistance in the church and the monastic buildings, moving slowly, but as confident as a sighted man, familiar with every pillar and flagstone. Now he sang a note in his rich baritone, and the choir began a hymn.

Merthin was quietly sceptical about the clergy. Priests had power that was not always matched by their knowledge – rather like his employer, Elfric. However, he liked going to church. The services induced a kind of trance in him. The music, the architecture and the Latin incantations enchanted him, and he felt as if he were asleep with his eyes open. Once again he had the fanciful sensation that he could feel the rainwater flowing in torrents far beneath his feet.

His gaze roamed over the three levels of the nave – arcade, gallery and clerestory. He knew that the columns were made by placing one stone on top of another, but they gave a different impression, at least at first glance. The stone blocks were carved so that each column looked like a bundle of shafts. He traced the rise of one of the four giant piers of the crossing, from the huge square foot on which it stood, up to where one shaft branched north to form an arch across the side aisle, on up to the tribune level where another shaft branched west to form the arcade of the gallery, on up to the westward springing of a clerestory arch, until the last remaining shafts separated, like a spray of flowers, and became the curving ribs of the ceiling vault far above. From the central boss at the highest point of the vault, he followed a rib all the way down again to the matching pier on the opposite corner of the crossing.

As he did so, something odd happened. His vision seemed momentarily to blur, and it looked as if the east side of the transept moved.

There was a low rumbling sound, so deep it was almost inaudible, and a tremor underfoot, as if a tree had fallen nearby.

The singing faltered.

In the chancel, a crack appeared in the south wall, right next to the pier Merthin had been looking at.

He found himself turning towards Caris. Out of the corner of his eye he saw masonry falling in the choir and the crossing. Then there was nothing but noise: women screaming, men shouting, and the deafening crash of huge stones hitting the floor. It lasted a long moment. When silence descended, Merthin found he was holding Caris, his left arm around her shoulders pressing her to him, his right arm protectively covering her head, his body interposed between her and the place where a part of the great church lay in ruins.

It was obviously a miracle that no one died.

The worst of the damage was in the south aisle of the chancel, which had been empty of people during the service. The congregation was not admitted to the chancel, and the clergy had all been in the central part, called the choir. Several monks had had narrow escapes, which only heightened the talk of miracles, and others had bad cuts and bruises from flying chips of stone. The congregation suffered no more than a few scratches. Evidently, they had all been supernaturally protected by St Adolphus, whose bones were preserved under the high altar, and whose deeds included many instances of curing the sick and saving people from death. However, it was generally agreed that God had sent the people of Kingsbridge a warning. What he was warning them about was not yet clear.

An hour later, four men were inspecting the damage. Brother Godwyn, the cousin of Caris, was the sacrist, responsible for the church and all its treasures. Under him as matricularius, in charge of building operations and repairs, was Brother Thomas, who had been Sir Thomas Langley ten years ago. The contract for cathedral maintenance was held by Elfric, a carpenter by training and a general builder by trade. And Merthin tagged along as Elfric’s apprentice.

The east end of the church was divided by pillars into four sections, called bays. The collapse had affected the two bays nearest the crossing. The stone vaulting over the south aisle was destroyed completely in the first bay and partially in the second. There were cracks in the tribune gallery, and stone mullions had fallen from the windows of the clerestory.

Elfric said: “Some weakness in the mortar allowed the vault to crumble, and that in turn caused the cracks at higher levels.”

That did not sound right to Merthin, but he lacked an alternative explanation.

Merthin hated his master. He had first been apprenticed to Elfric’s father, Joachim, a builder of wide experience who had worked on churches and bridges in London and Paris. The old man had delighted in explaining to Merthin the lore of the masons – what they called their ‘mysteries’, which were mostly arithmetical formulas for building, such as the ratio between the height of a building and the depth of its foundations. Merthin liked numbers and lapped up everything Joachim could teach him.

Then Joachim died, and Elfric took over. Elfric believed the main thing an apprentice had to learn was obedience. Merthin found this difficult to accept, and Elfric punished him with short rations, thin clothing and outdoor work in frosty weather. To make matters worse, Elfric’s chubby daughter Griselda, the same age as Merthin, was always well fed and warmly dressed.

Three years ago Elfric’s wife had died, and he had married Alice, the older sister of Caris. People thought Alice was the prettier sister, and it was true that she had more regular features, but she lacked Caris’s captivating ways, and Merthin found her dull. Alice had always seemed to like Merthin almost as much as her sister did, and so he had hoped she would make Elfric treat him better. But the reverse happened. Alice seemed to think it was her wifely duty to join with Elfric in tormenting him.

Merthin knew that many other apprentices suffered in the same way, and they all put up with it because apprenticeship was the only way into a well-paid trade. The craft guilds efficiently kept out upstarts. No one could do business in a town without belonging to a guild. Even a priest, a monk or a woman who wanted to deal in wool or brew ale for sale would have to get into a guild. And outside the towns there was little business to be done: peasants built their own houses and sewed their own shirts.

At the end of the apprenticeship, most boys would remain with the master, working as journeymen for a wage. A few would end up partners, taking over the enterprise when the old man died. That would not be Merthin’s destiny. He hated Elfric too much. He would leave the moment he could.

“Let’s look at it from above,” said Godwyn.

They walked towards the east end. Elfric said: “It’s good to see you back from Oxford, Brother Godwyn. But you must miss the company of all those learned people.”

Godwyn nodded. “The masters are truly astonishing.”

“And the other students – they must be remarkable young men, I imagine. Though we hear tales of bad behaviour, too.”

Godwyn looked rueful. “I’m afraid some of those stories are true. When a young priest or monk is away from home for the first time, he may suffer temptation.”

“Still – we’re fortunate to have the benefit of university-trained men here in Kingsbridge.”

“Very kind of you to say so.”

“Oh, but it’s true.”

Merthin wanted to say: Shut up, for pity’s sake. But this was Elfric’s way. He was a poor craftsman, his work inaccurate and his judgement shaky, but he knew how to ingratiate himself. Merthin had watched him do it, time and again – for Elfric could be as charming to people from whom he wanted something as he could be rude to those who had nothing he needed.