"I do not ask you to. This morning Matrusus ordered the house of Pudens, where we had gathered in prayer, burnt over our heads. Some Christians were burnt alive, afterwards others were tortured by Matrusus, horribly tortured. He carves the sign of the Cross, which is holy to us, upsidedown, in blood . . ." She shuddered. "I hear Pudens screaming still."

Heedless of her filth, Quistus took her hand. "But something even worse than that has happened, hasn't it?"

She nodded, squeezing his fingers tight.

"Matrusus has been murdered."

"Omba, stay here." Quistus crossed the courtyard of the Villa Marcia.

"Me, stay?" she called. "I'm not staying. Who would look after you?"

He whistled from the gate. The Vicus Armilustri was a wealthy street and at once a waiting sedan chair of the Subura cartel, the "family" of Vitellius, was lifted and run smartly to him. The slaves hefting the poles were the usual hairy barbarians, broken-down warriors from forgotten wars, the blind one at the back, and at the front the one with eyes but no arms, lifting with a neck-sling. There was nothing wrong with their muscle-strapped legs.

"Pomegranate Street." Quistus handed Volusia aboard. "The house of Pudens, near the Basilica Opimia." The blind one nodded eagerly, carrying a map of Rome in his head. "Run all the way and there's an extra penny for you, each. And I won't tell Vitellius."

The men heaved the weight, taking the uphill slope at a run. Volusia sat on the narrow bench opposite him, their knees almost touching. He looked out. "They'll take away Matrusus's body soon. The praetor urbanus will decide if there is a case to answer. A prosecutor will be appointed. I've got to get there first."

"Why?"

Still he wouldn't look at her. "There may be signs that tell us what really happened. Perhaps that Matrusus was indeed murdered by Pudens, or by your father. Or not, as you say."

"We believe in peace. It is impossible for a Christian to commit murder. We are the Lambs."

He said nothing.

"What's the matter?" she asked. "You're so pale."

He gazed at the crowds pushing and shoving. "Your clean clothes. Omba gave you my wife's clothes to wear." "Does it offend you?"

He looked from the window. "It . . . reminds me." "Marcia."

"Yes. That was her name."

"You have no idea at all?"

"Not one clue. Death is not reasonable, perhaps."

"In your military career and as a diplomat you must have known many men die." The coffee would not let Volusia go. "Perhaps death follows you," she blurted. "That must be hard for a logician to accept."

"Logic is simply a way of discovering the truth." "To discover truth you must become a Christian."

"I believe death always has a reason." No sign of Omba following them, but he knew she'd be close, no one knew the back ways of Rome like Omba. He closed the curtains, suddenly hating the crowds. "Sometimes a reason is so hard to discover. I am Septimus because I am my father's seventh son, it was his pet name for me. Now I can hardly bear to hear it said. My own seventh son is Septimus."

"Is?"

"His body was not found with the others."

"What does that tell a logician?"

"That Septimus is still alive."

"Isn't that a father's faith, desperate hope, not logic?" The curtains blew open in the wind and he closed them. "Logic says perhaps he killed them."

"All of them?"

"His sister was not found. Perhaps they both killed their brothers and their mother and ran away together." He shrugged. "Perhaps there is no reason or logic to be found. Perhaps it just . . . happened."

"My father did not kill Matrusus."

"Then," Quistus said, "in order to prove that, we have to prove who did." And he ignored her angry stare.

The sedan stopped, dropped. A knock on the roof. "No further can we go," called the blind man's heavy German accent. "My penny now please sir."

Quistus gazed across the heads of the crowd as he paid the fare, tossed the men an extra penny each. The house of Pudens was burned out. A flapping sound in the sky: the apartment blocks on each side attracted the wind, setting the washing flying and twisting on the ropes strung between them. "Keep close." Towing Volusia after him, muttering an apology to the bald-headed man he knocked aside, Quistus pushed to the front. He tapped the Guard on his greasy shoulder. "Let me pass."

"Piss off."

Sword clenched in hand, the body of Matrusus lay where it fell, outstretched on the cobbles, rubbish blowing past it, cloak rippling like living blood. The spear-shaft standing between his eyes nodded gently in the wind, its movement making Matrusus appear oddly alive, wisely nodding at his own death. "I want carts! And carpenters!" A squat man gave orders to soldiers and scribes. "I want crosses. Yes, crosses."

Quistus murmured, "Stigmus. I feared it." He called, "Stigmus!"

"You?" The squat man turned. "Are you mad? Are you with these people?"

"Let me through."

"Stay away, Septimus Severus Quistus. You can do no good here."

"I am merely curious."

"Curious? I thought you were dead. Yes, pass him." He beckoned.

"Stay out of sight," Quistus whispered to Volusia. "Stigmus and I go back." But she exclaimed, seeing her father lined up with the other Christian rebels by the wall, their clothes torn, trembling and nervous. They had not been lightly treated. Several men had the shape of a cross cut into their heads, still trickling. Their wives held the wounds closed.

"Father! Mother!" Volusia twisted from his grasp, ran to Pedilla and Faustinus, embraced them. Stigmus watched attentively, saw enough, then moved his hand lightly in command. Two soldiers dragged Volusia to the end of the line, threw her down. "A touching reunion. Thank you, my dear Quistus. Another fish drawn into my net to wait her turn."

"She's done nothing wrong, Stigmus."

"Fish, yet another secret name of these Christian martyrs, did you not know? Graffiti of the Fish are scrawled on street corners everywhere. It will stop. I will stop them."

If any man could, Quistus knew, that man was Stigmus. The prosecutor was forty-five years old, thickset, powerful, determined, ambitious. His grey hair was tightly curled across his forehead, his square face surprisingly intelligent, slightly too red, faintly debauched. His eyes were cold, dark stones.

"Let her go, Stigmus. She doesn't belong here."

"She's a Christian. Promise me she hasn't involved you. This is a bad place."

"Do you know what happened?"

"A Christian riot."

"You know Matrusus better than that."

"Knew." Stigmus moved one hand from the folds of his toga, gestured at the body, but his eyes did not move. "Murdered."

"He was a murderer many times over."

"Killed by a single spear thrust through the face. Directly between the eyes. Perfect symmetry. One can only admire these Christians' skill and strength and astonishing precision, as well as their viciousness."

"He won't be missed."

"The Emperor will miss him. Nero cried when he heard. Do not get mixed up with Christians, my friend." By friend Stigmus meant enemy. "I warn you, the Emperor is interested. Personally. I have full powers of investigation."

"I can guess what the result will be."

"I'm a fair man. As usual they will be asked to invoke our gods, worship the image of Nero, and curse Christ. If they refuse they are guilty and I shall crucify them as their god was crucified, except upside-down. They hate that. They believe in an underworld, a place of fire and torture called Hell, and they don't want to fall to it head-first."

"All of them? A spear can fly from only one pair of hands." "They say they're all guilty. In the next breath they say they're all innocent." He shook his head in disgust. "They want to die. It's the same in all these pagan religions, they all believe in death. Die, be happy. You know their Christ preached revolution? Destruction of the Jerusalem Temple. His closest advisers were zealots, assassins, the poor - desperate enough to do anything. Don't believe a word Christians say."

"Why does Nero hate them so?"

"Because he is tolerant and they are not. Their God excludes all other gods - including the Emperor, who is of course a god, pater, Pope, Pontifex Maximus, the bridge between this world and the next, married to immortal Rome. When Nero dies he will rise again, redivivus - an idea the Christians have actually stolen for their own Christ! Blasphemy."

"Stigmus -"

"You know what your Christians call our Emperor? The Beast. Worse names. 666. Satan. You can't expect him to love them for it."

"Who carved the cross on their foreheads?"

"Matrusus's signature. You know his sense of fun. A blood cross. They call it the mark of the Beast."

"I need to examine the body."

"They killed him, and that's that. Matrusus died unnecessarily, they will die legally and horribly. Now, I have an interrogation to conduct." Stigmus threw back over his shoulder, "You're wasting your time!"

Quistus knelt. Matrusus stared at the sky. The spear had pierced him exactly between his eyes - as Stigmus said, with absolute precision. Almost eerie precision. Very skilled. Would Faustinus the merchant, thin and looking the far side of fifty, have such strength, such skill? Pedilla his wife, or Volusia? One of the soldiers was calling their names, a scribe writing them down. Linus might be strong enough. What about Timothy, who crouched away from the women? The one called Peter was too old. Pudens looked like an intellectual, a poet, but he sat beside a strong-looking redheaded woman.

"Claudia, his wife." Omba grunted, kneeling. "I checked, Master. Everyone's eager to talk. The daughter of old King Caractacus of Britannia, they say."

"A Roman citizen?"

"Pudens is, so she married one, she's protected by citizen law."

"Not much protection for long." Quistus closed his hands around the shaft of the spear. "Are you thinking what I'm thinking?"

"It's too thick, too long, too heavy."

"That's because" - Quistus placed his sandalled foot on Matrusus, tugged hard on the shaft, withdrawing it with a soggy sucking sound - "it isn't a spear."

He wiped the brains off the end. Blunt sawn wood. "It's a pole." Omba shook her head, impressed. "Someone very strong threw that thing. Phew."

Quistus turned his gaze from the Christians, raised his eyes to the washing flapping in the sky between the apartment blocks, the Exelsius on one side, the Imperium on the other. "It's a washing-pole." He pointed at a rope, still with washing attached, hanging down from the top corner of the Exelsius, then turned back to the Imperium. No pole, no rope.

"No," Omba said. "I'm not climbing up there, not me."

The Imperium doorkeeper had fled. Light in the lobby came from above, down the light-well in the centre of the building. Quistus climbed the stairs past sturdy apartment doors, came out on the flat roof. He hung on as the wind gusted, about eighty feet above the street. The roof of the Imperium was laid out like a small garden, carefully-tended shrubs, a trellis, a few benches, a pleasant place to relax on a summer evening but cold and breezy now. At each corner a washing-pole stood bedded in mortar, an endless line leading from the tip to another apartment block.

Except this corner. Quistus leaned out. Even Omba looked small, far below. He narrowed his eyes, peering across at the cream stucco of the Exelsius's seven storeys. A mark on the corner just over half way down. He returned downstairs.

"Well? Thrown from up there?" Omba asked.

Without a word Quistus crossed to the Exelsius. He climbed three floors, orientated himself, then knocked on a door. It swung open. An old woman sat with a cat on her lap. "I thought you were my breakfast," she said. "But you don't sound like my daughter."

"Did you hear the trouble last night, mother?"

"No, nothing."

He stepped onto the balcony, reached out past the dangling, frayed end of the line to the gash in the stucco. Fresh. The end of something rounded had struck against the wall here, very hard - hard enough to break the line. He stared down, eyes searching. "Nothing at all?"

"No." The blind woman stroked her cat. "At night I sleep. With my ears closed. It's safer."

"Thank you, mother."

He closed the door and went downstairs to the street. He stood by Matrusus's feet, on the exact spot Matrusus was standing when he was hit. It didn't make sense. Then he saw the slope-roofed outhouse leaning against the ground floor of the Imperium. His eye traced an imaginary line. It beggared belief; but it had to be true.

He looked round, realizing everyone was watching. "Don't keep me waiting," Stigmus said.

Quistus gathered his thoughts. "Let him think!" Omba sounded proud, almost maternal. "That's what my master does best, he does."

"Keep her quiet," Stigmus said.

"You can't keep me quiet," Omba said.

Quistus spoke. "The fact is, none of the Christians was strong enough to do this to Matrusus on the ground. To have shoved this blunt pole - not a spear - through his face would have required someone as strong as Matrusus himself. And why didn't Matrusus defend himself? His sword was drawn."

"Everyone can see the pole was thrown from a distance," Stigmus said. "His sword was no defence."

"The pole was thrown from up there." Quistus moved a few steps from Matrusus, pointing up at the top corner of the Imperium that came into view.

Stigmus said, "The killer couldn't even have seen his target! How could he aim? This is nonsense!"

"The wind killed Matrusus." Quistus pointed at the washing line down the wall of the Exelsius. "There was a gust, the line was heavy with washing, the pole broke out of the mortar. As it fell fifty, sixty feet the attached line swung it like a slingshot towards the Exelsius. The pole struck the wall by the balcony with terrific force, breaking the line -"

"This is ridiculous! Still not in sight of Matrusus! How could it hit him?"

"The pole span downward, struck the sloping roof of that outhouse at just the right angle, then span outward on the new trajectory. Matrusus never knew what hit him."

"Hit him with incredible accuracy. How do you account for that?" Stigmus was furious. "It beggars belief. I'll tear the truth out of them."

"Stigmus, it was an accident," Quistus said. "Pure chance."