Elfric snorted sceptically, but the other builders looked intrigued. The two boys reached midstream, touched the central pier, took deep breaths and disappeared.

Merthin said: “When they come back, they will tell us that the pier is not resting on the river bed, but hanging over a depression, filled with water, large enough for a man to climb into.”

He hoped he was right.

Both boys stayed under water for a surprisingly long time. Merthin found himself feeling breathless, as it were in sympathy with them. At last a wet head of red hair broke the surface, then a brown one. The two boys conversed briefly, nodding, as if establishing that they had both observed the same thing. Then they struck out for the shore.

Merthin was not completely sure of his diagnosis, but he could think of no other explanation for the cracks. And he had felt the need to appear supremely confident. If he now turned out to be wrong, he would look all the more foolish.

The boys reached the bank and waded out of the water, panting. Madge gave them blankets which they pulled around their shaking shoulders. Merthin allowed them a few moments to catch their breath, then said: “Well? What did you find?”

“Nothing,” said Dennis, the elder.

“What do you mean, nothing?”

“There’s nothing there, at the bottom of the pillar.”

Elfric looked triumphant. “Just the mud of the river bed, you mean.”

“No!” said Dennis. “No mud – just water.”

Noah put in: “There’s a hole you could climb into – easily! That big pillar is just hanging in the water, with nothing under it.”

Merthin tried not to look relieved.

Elfric blustered: “There’s still no authority for saying a pile of loose stones would have solved the problem.” But no one was listening to him. In the eyes of the crowd, Merthin had proved his point. They gathered around him, commenting and questioning. After a few moments, Elfric walked away alone.

Merthin felt a momentary pang of compassion. Then he recalled how, when he was an apprentice, Elfric had hit him across the face with a length of timber; and his pity evaporated into the cold morning air.

56

The following morning, a monk came to see Merthin at the Bell. When he pulled back his hood, Menhin did not at first recognize him. Then he saw that the monk’s left arm was cut off at the elbow, and he realized it was Brother Thomas, now in his forties, with a grey beard and deep-set lines around his eyes and mouth. Was his secret still dangerous after all these years, Merthin wondered? Would Thomas’s life be in danger, even now, if the truth came out?

But Thomas had not come to talk about that. “You were right about the bridge,” he said.

Merthin nodded. There was a sour satisfaction in it. He had been right, but Prior Godwyn had fired him, and in consequence his bridge would never be perfect. “I wanted to explain the importance of the rough stones, back then,” he said. “But I knew Elfric and Godwyn would never listen to me. So I told Edmund Wooler, then he died.”

“You should have told me.”

“I wish I had.”

“Come with me to the church,” Thomas said. “Since you can read so much from a few cracks, I’d like to show you something, if I may.”

He led Merthin to the south transept. Here and in the south aisle of the choir Elfric had rebuilt the arches, following the partial collapse eleven years ago. Merthin saw immediately what Thomas was worrying about: the cracks had reappeared.

“You said they would come back,” Thomas said.

“Unless you discovered the root cause of the problem, yes.”

“You were right. Elfric was wrong twice.”

Merthin felt a spark of excitement. If the tower needed rebuilding… “You understand that, but does Godwyn?”

Thomas did not answer the question. “What do you think the root cause might be?”

Menhin concentrated on the immediate problem. He had thought about this, on and off, for years. “This is not the original tower, is it?” he said. “According to Timothy’s Book, it has been rebuilt, and made higher.”

“About a hundred years ago, yes – when the raw wool business was booming. Do you think they made it too high?”

“It depends on the foundations.” The site of the cathedral sloped gently to the south, towards the river, and that might be a factor. He walked through the crossing, under the tower, to the north transept. He stood at the foot of the massive pillar at the north-east corner of the crossing and looked up at the arch that stretched over his head, across the north aisle of the choir, to the wall.

“It’s the south aisle I’m worried about,” Thomas said, slightly peevishly. “There are no problems here.”

Merthin pointed up. “There’s a crack on the underside of the arch – the intrados – at the crown,” he said. “You get that in a bridge, when the piers are inadequately grounded and start to splay apart.”

“What are you saying – that the tower is moving away from the north transept?”

Merthin went back through the crossing and looked at the matching arch on the south side. “This one is cracked, too, but on the upper side, the extrados, do you see? The wall above it is cracked, too.”

“They aren’t very big cracks.”

“But they tell us what is happening. On the north side, the arch is being stretched; on the south side, it’s being pinched. That means the tower is moving south.”

Thomas looked up warily. “It seems straight.”

“You can’t see it with the eye. But if you climb up into the tower, and drop a plumb line from the top of one of the columns of the crossing, just below the springing of the arch, you will see that by the time the line touches the floor it will be adrift of the column to the south by several inches. And, as the tower leans, it’s separating from the wall of the choir, which is where the damage shows worst.”

“What can be done?”

Merthin wanted to say: You have to commission me to build a new tower. But that would have been premature. “A lot more investigation, before any building,” he said, suppressing his excitement. “We have established that the cracks have appeared because the tower is moving – but why is it moving?”

“And how will we learn that?”

“Dig a hole,” Merthin said.

In the end Jeremiah dug the hole. Thomas did not want to employ Merthin directly. It was difficult enough as it was, he said, to get the money for the investigation out of Godwyn, who seemed never to have any money to spare. But he could not give the job to Elfric, who would have said there was nothing to investigate. So the compromise was Merthin’s old apprentice.

Jeremiah had learned from his master and liked to work fast. On the first day, he lifted the paving stones in the south transept. Next day, his men started excavating the earth around the huge south-east pier of the crossing.

As the hole got deeper, Jeremiah built a timber hoist for lifting out loads of earth. By the second week he had to build wooden ladders down the sides of the hole so that the labourers could get to the bottom.

Meanwhile, the parish guild gave Merthin the contract for the repair of the bridge. Elfric was against the decision, of course, but he was in no position to claim that he was the best man for the job, and he hardly bothered to argue.

Merthin went to work with speed and energy. He built cofferdams around the two problem piers, drained the dams and began to fill the holes under the piers with rubble and mortar. Next he would surround the piers with the piles of large rough stones he had envisaged from the start. Finally, he would remove Elfric’s ugly iron braces and fill the cracks with mortar. Provided the repaired foundations were sound, the cracks would not reopen.

But the job he really wanted was the rebuilding of the tower.

It would not be easy. He would have to get his design accepted by the priory and the parish guild, currently run by his two worst enemies, Godwyn and Elfric. And Godwyn would have to find the money.