“I’m entirely at your service, Father.”

“Thank you, my son. We’ve had this sort of trouble before, d’ye see, over the head of the excavations and all. Rat trouble. Though Brother Dominic’s been after them in a very big way and it was our belief they were exterminated. And wouldn’t we look the fools if we’d stirred up Signor Bergarmi and his body of men and they fully occupied with their task?”

“Shall we have a look where the trouble seems to be?”

“A look, is it? A smell, more likely. But come along, come along.”

As he made that downward journey for the third time, it seemed to Alleyn that in its quiet way it was one of the strangest he had ever taken. A monk, a lay brother and himself, descending, if one cared to be fanciful, through a vertical section of the past.

When they reached the cloisters on the second level, Brother Dominic, who had not yet uttered a word, turned on the fluorescent lights and back into their immovable liveliness sprang the Apollo and the Mercury.

Down the iron spiral: two pairs of sandals and one pair of leather soles with the ever mounting sound of flowing water. The bottom level and a right turn. This was where Kenneth Dorne had parted company with Sebastian Mailer. On their left was the little anteroom into the Mithraeum. Ahead — the lights came on — ahead, the sarcophagus and the railed well.

They walked towards them.

The lid had not been replaced. It stood on its side, leaning against the empty stone coffin where Violetta had been urgently housed.

Father Denys put his hand on Alleyn’s arm.

“Now,” he said and they stopped.

“Yes,” Alleyn said.

It declared itself: sweetish, intolerable, unmistakable.

He went on alone, leant over the top rail where yesterday he had found a fragment of cloth and looked into the well, using the torch they had given him.

It showed walls in a sharp perspective and at the bottom an indefinable darkness.

“The other day,” he said, “when I looked down, there was a sort of glint. I took it to be a chance flicker of light on the moving stream.”

“It could be that.”

“What is there — down below?”

“The remains of a stone grille. As old,” Father Denys said, “as the place itself. Which is seventeen hundred years. We’ve lowered a light and it revealed nothing that you could call of any consequence but it was too far beneath to be of any great help.”

“The grille is above the surface of the stream?”

“It is. A few inches at the downstream end of the well. And it’s the remains only. A fragment you may say.”

“Could something have been carried down by the stream and got caught up in it?”

“It’s never been known in the history of this place. The water is pure. Every so often we let down a wee tin and haul up a sample for the testing. There’s never been the hint of contamination in it.”

“Can one get down there?”

“Well — now—”

“I think I can see footholds and — yes—”

Brother Dominic spoke. “You can,” he said.

“Aren’t there iron pegs?”

“There are.”

“And they rotten no doubt,” Father Denys urged, “and falling out like old teeth at the first handling.”

“Have you a rope, Father?”

“Sure, we have them for the excavations. You’re not thinking—”

“I’ll go down if you’ll give me a hand.”

“Dominic, let you fetch a rope?”

“And a head-lamp and overalls,” Brother Dominic enumerated with a glance at Alleyn’s impeccable suit. “We have them all got. I’ll fetch them, Father.”

“Do so.”

“It’s unwholesome here,” Father Denys said when Brother Dominic had gone. “Let us move away for the time being.”

They entered the Mithraeum. Father Denys had switched on the lighting used in visiting hours. The altar glowed. At the far end, the god, lit from beneath, stared out of blank eyes at nothing. They sat on one of the stone benches where in the second century his initiates had sat, wan with their ordeal, their blanched faces painted by the altar fires.

Alleyn thought he would like to ask Father Denys what he made of the Mithraic cult but when he turned to speak to him found that he was withdrawn into himself. His hands were pressed together and his lips moved.

Alleyn waited for a minute and then, hearing the returning slap of sandals in the cloister, went quietly out by the doorway behind the god. This was the passage by which he and the Van der Veghels had left the Mithraeum. It was very dark indeed and the Baroness had exclaimed at it.

Two right turns brought him back into sight of the well and there was Brother Dominic with ropes, an old-fashioned head-lamp of the sort miners use, a suit of workmen’s overalls and a peculiar woolly cap.

“I’m obliged to you, Brother Dominic,” said Alleyn.

“Let you put them on.”

Alleyn did so. Brother Dominic fussed about him. He fixed the head-lamp and with great efficiency made fast one end of the rope round Alleyn’s chest and under his shoulders.

Alleyn transferred a minuscule camera from his homicide kit to the pocket of his overalls. After looking about for a minute, Brother Dominic asked Alleyn to help him place the lid of the sarcophagus at right angles across the coffin. It was massive but Brother Dominic was a strong man and made little of it. He passed the slack of the rope twice round the lid, crossing it in the manner of sailors when they wear a rope in lowering a heavy load.

“We could take your weight neat between us,” he said, “but this will be the better way. Where’s Father?”

“In the Mithraeum. Saying his prayers, I think.”

“He would be that.”

“Here he is.”

Father Denys returned looking anxious.

“I hope we are right about this,” he said. “Are you sure it’s safe, now, Dominic?”

“I am, Father.”

“Mr. Alleyn, would you not let me place a — a handkerchief over your — eh?”

He hovered anxiously and finally did tie his own large cotton handkerchief over Alleyn’s nose and mouth.

The two Dominicans tucked back their sleeves, wetted their palms and took up the rope, Brother Dominic on Alleyn’s side of the sarcophagus lid and Father Denys on the far side, close to the turn. “That’s splendid,” Alleyn said. “I hope I won’t have to trouble you. Here I go.”

“God bless you,” they said in their practical way.

He had another look at the wall. The iron pegs went down at fairly regular intervals on either side of one corner. The well itself was six feet by three. Alleyn ducked under the bottom rail, straddled the corner with his back to the well, knelt, took his weight on his forearms, wriggled backwards and groped downwards with his right foot.

“Easy now, easy,” said both the Dominicans. He looked up at Brother Dominic’s sandalled feet, at his habit and into his long-lipped Irish face. “I have you held,” said Brother Dominic and gave a little strain on the rope to show that it was so.

Alleyn’s right foot found a peg and rested on it. He tested it, letting himself down little by little. He felt a gritting sensation and a slight movement under his foot but the peg took his weight.

“Seems O.K.,” he said through Father Denys’s handkerchief.

He didn’t look up again. His hands, one after the other, relinquished the edge and closed, right and then left, round pegs. One of them tilted, jarred and ground its way out of its centuries-old housing. It was loose in his hand and he let it fall. So long, it seemed, before he heard it hit the water. Now he had only one handhold and his feet but the rope sustained him. He continued down. His face was close to the angle made by the walls and he must be careful lest he knock his headlamp against stone. It cast a circle of light that made sharp and intimate the pitted surface of the rock. Details of colour, irregularities and growths of some minute lichen passed upwards through the light as he himself so carefully sank.

Already the region above seemed remote and the voices of the Dominicans disembodied. His world was now filled with the sound of running water. He would have smelt water, he thought, if it had not been for that other growing and deadly smell. How far had he gone? Why hadn’t he asked Brother Dominic for the actual depth of the well? Thirty feet? More? Would the iron pegs have rusted and rotted in the damper air?