There were several important visiting clergymen in the choir for the service – Bishop Henri of Shiring, Archbishop Piers of Monmouth and Archdeacon Reginald of York – and presumably Philemon was hoping to impress them with this outburst of doctrinal conservatism. But to what end? Was he looking for promotion? The archbishop was ill – he had been carried into the church – but surely Philemon could not aspire to that post? It was something of a miracle that the son of Joby from Wigleigh should have risen to be prior of Kingsbridge. Besides, elevation from prior to archbishop would be an unusually big jump, a bit like going from knight to duke without becoming a baron or an earl in between. Only a special favourite could hope for such a rapid rise.

However, there was no limit to Philemon’s ambition. It was not that he felt himself to be superbly well qualified, Caris thought. That had been Godwyn’s attitude, arrogant self-confidence. Godwyn had assumed that God made him prior because he was the cleverest man in town. Philemon was at the opposite extreme: in his heart he believed he was a nobody. His life was a campaign to convince himself that he was not completely worthless. He was so sensitive to rejection that he could not bear to consider himself undeserving of any post, no matter how lofty.

She thought of speaking to Bishop Henri after the service. She might remind him of the ten-year-old agreement that the prior of Kingsbridge had no jurisdiction over the hospital of St Elizabeth on Leper Island, which came under the bishop’s direct control; so that any attack on the hospital was an attack on the rights and privileges of Henri himself. But, on further reflection, she realized that such a protest would confirm to the bishop that she was conducting dissections, and turn what might now be only a vague suspicion, easily ignored, into a known fact that must be dealt with. So she decided to remain silent.

Standing beside her were Merthin’s two nephews, the sons of Earl Ralph: Gerry, age thirteen, and Roley, ten. Both boys were enrolled in the monks’ school. They lived in the priory but spent much of their free time with Merthin and Caris at their house on the island. Merthin had his hand resting casually on the shoulder of Roley. Only three people in the world knew that Roley was not his nephew but his son. They were Merthin himself, Caris, and the boy’s mother, Philippa. Merthin tried not to show special favour to Roley, but found it hard to disguise his true feelings, and was especially delighted when Roley learned something new or did well at school.

Caris often thought about the child she had conceived with Merthin and then aborted. She always imagined it to have been a girl. She would be a woman now, Caris mused, twenty-three years old, probably married with children of her own. The thought was like the ache of an old wound, painful but too familiar to be distressing.

When the service was over they all left together. The boys were invited to Sunday dinner, as always. Outside the cathedral, Merthin turned to look back at the tower that now soared high over the middle of the church.

As he examined his almost-finished work, frowning at some detail visible only to him, Caris studied him fondly. She had known him since he was eleven years old, and had loved him almost as long. He was forty-five now. His red hair was receding from his brow, and stood up around his head like a curly halo. He had carried his left arm stiffly ever since a small carved stone corbel, dropped from the scaffolding by a careless mason, had fallen on his shoulder. But he still had the expression of boyish eagerness that had drawn the ten-year-old Caris to him on All Hallows’ Day a third of a century ago.

She turned to share his view. The tower appeared to stand neatly on the four sides of the crossing, and to be exactly two bays square, even though in fact its weight was held up by massive buttresses built into the exterior corners of the transepts, which themselves rested on new foundations separate from the old original ones. The tower looked light and airy, with slender columns and multiple window openings through which you could see blue sky in fine weather. Above the square top of the tower, a web of scaffolding was rising for the final stage, the spire.

When Caris brought her gaze back down to ground level she saw her sister approaching. Alice was only a year older at forty-five, but Caris felt she was from another generation. Her husband, Elfric, had died in the plague, but she had not remarried, becoming frumpy, as if she thought that was how a widow should be. Caris had quarrelled with Alice, many years ago, over Elfric’s treatment of Merthin. The passage of time had blunted the edge of their mutual hostility, but there was still a resentful tilt to Alice’s head when she said hello.

With her was Griselda, her stepdaughter, though only a year younger than Alice. Griselda’s son, known as Merthin Bastard, stood beside her, towering over her, a big man with superficial charm – just like his father, the long-gone Thurstan, and about as different from Merthin Bridger as could be. Also with her was her sixteen-year-old daughter, Petranilla.

Griselda’s husband, Harold Mason, had taken over the business after Elfric died. He was not much of a builder, according to Merthin, but he was doing all right, although he did not have the monopoly of priory repairs and extensions that had made Elfric rich. He stood next to Merthin now and said: “People think you’re going to build the spire with no formwork.”

Caris understood. Formwork, or centering, was the wooden frame that held the masonry in place until the mortar dried.

Merthin said: “Not much room for formwork inside that narrow spire. And how would it be supported?” His tone was polite, but Caris could tell from its briskness that he did not like Harold.

“I could believe it if the spire was going to be round.”

Caris understood this, too. A round spire could be built by placing one circle of stones on top of another, each a little narrower than the last. No formwork was needed because the circle was self-supporting: the stones could not fall inwards because they pressed on one another. The same was not true of any shape with corners.

“You’ve seen the drawings,” Merthin said. “It’s an octagon.”

The corner turrets on the top of the square tower faced diagonally outwards, easing the eye as it progressed upwards to the different shape of the narrower spire. Merthin had copied this feature from Chartres. But it made sense only if the tower was octagonal.

Harold said: “But how can you build an octagonal tower without formwork?”

“Wait and see,” said Merthin, and he moved away.

As they walked down the main street Caris said: “Why won’t you tell people how you’re going to do it?”

“So that they can’t fire me,” he replied. “When I was building the bridge, as soon as I’d done the hard part they got rid of me, and hired someone cheaper.”

“I remember.”

“They can’t do that now, because no one else can build the spire.”

“You were a youngster then. Now you’re alderman. No one would dare sack you.”

“Perhaps not. But it’s nice to feel they can’t.”

At the bottom of the main street, where the old bridge had stood, there was a disreputable tavern called the White Horse. Caris saw Merthin’s sixteen-year-old daughter, Lolla, leaning on the wall outside, with a group of older friends. Lolla was an attractive girl, with olive skin and lustrous dark hair, a generous mouth and sultry brown eyes. The group was crowded around a dice game, and they were all drinking ale from large tankards. Caris was sorry, though not surprised, to see her stepdaughter carousing on the street at midday.

Merthin was angry. He went up to Lolla and took her arm. “You’d better come home for your dinner,” he said in a tight voice.