"Jesus," said Mark. He leaned against the door-jamb to steady himself, and took three or four very deep breaths. "Jesus."

Katie was hysterical. "What's happened to him? Mark - what's happened to him?"

"I don't know. I just don't know." He took hold of her, awkwardly, and tried to hold her close, but she couldn't stop twitching and trembling; and she kept twisting her head around to stare at Nigel, as if she had to look at his mutilated body, to convince herself that he was really dead. Katie stared at Mark wild-eyed. "What if it's a dog - it must be still in here, somewhere!"

Mark led her through to the kitchen and rattled the back door handle, to show her that it was still secure. "I locked it myself, last night. Whatever it was, it isn't here any more. Wait there. I'll have to call the police."

He had left his phone on the blood-spattered coffee table next to Nigel's body. He stepped cautiously around the couch and picked it up. He couldn't take his eyes off Nigel's face. The strange thing was, Nigel didn't look terrified. In fact, he looked almost exultant, as if having his throat ripped out had been the most thrilling experience of his whole life.

Katie came through from the kitchen and stood in the doorway. She looked calmer now, although she was still trembling, and her face was as white as wax.

"Have you called them?" she asked him.

"I'm just about to."

"Mark... what do you really think it was?"

Mark's finger was poised over his phone, but he hesitated. "I can't imagine. But there's nobody else in the house, is there, apart from us? I hope the police won't think - "

And he suddenly thought about something else, too. The questions that the police would ask them, about the mirror. Technically, they had stolen it. An ancient relic, worth millions. So what would Nigel's death look like, at first sight, but a falling-out amongst thieves? He lifted his hands, and there was blood on them, from his phone.

"Look," said Katie, very quietly.

Mark frowned down at the worn beige carpet. There was a trail of blotchy bloodstains leading from the side of the couch to the center of the room. At first sight he had taken them for random spatters, but now he could see that they were footprints. Not Nigel's footprints, though. They were far too small, and there was no blood on Nigel's socks. Close to the coffee-table the footprints formed a pattern like a huge, petal-shedding rose , and then, much fainter, they made their toward the mirror. Where they stopped.

Katie looked all around the room, frowning. Then she approached the mirror and peered into the shiny circle that she had cleaned yesterday evening. "It's... no."

"No what?"

"It's almost as if somebody killed Nigel and then they walked across the room and into the mirror."

"That's insane. People can't walk into mirrors."

"But these footprints... they don't go anywhere else, do they?"

They both looked up at the face of Lamia. She looked back at them, secret and serene. Her smile seemed to say wouldn't you like to know?

"They built a tower, didn't they?" said Katie. "They built a to keep the Lady of Shalott locked up. If she was Lamia, then they locked her up because she seduced men and drank their blood."

"Katie, that was seven hundred years ago. That's if it really happened at all."

Katie pointed to Nigel's body on the couch. "Nigel's dead, Mark! That really happened! But nobody could have entered this house last night, could they? Not without breaking the door down and waking us up. Nobody could have entered this room unless they stepped right out of this mirror!"

"So what do we tell the police?"

"We tell them the truth, that's all."

"And you think they're going to believe us? 'Well, officer, it was like this. We took a thirteenth-century mirror that didn't belong to us and The Lady of Shalott came out of it in the middle of the night and tore Nigel's throat out?' They'll send us to Broadmoor, Katie! They'll put us in the funny farm for life!"

"Mark, listen, this is real. And these footprints... they prove it."

"It's only a story, Katie. It's only a legend."

"But think of the poem, The Lady of Shalott. Think of what it says. 'Moving thro' a mirror clear, that hangs before her all the year, shadows of the world appear.' Don't you get it? Tennyson specifically wrote through a mirror. Not in it - through it! The Lady of Shalott wasn't looking at her mirror, she was inside it, looking out!"

"This gets better."

"But it all fits together. She was Lamia. A blood-sucker, a vampire! Like all vampires, she could only come out at night. But she didn't hide inside a coffin all day... she hid inside a mirror! Daylight can't penetrate a mirror, any more than it can penetrate a closed coffin!"

"I don't know much about vampires, Katie, but I do know that you can't see them in mirrors."

"Of course not. And this is the reason why! Lamia and her reflection are one and the same. When she steps out of the mirror, she's no longer inside it, so she doesn't appear to have a reflection. And the curse on her must be that she can only come out of the mirror at night, like all vampires."

"Katie, for God's sake ... you're getting completely carried away."

"But it's the only answer that makes any sense! Why did they lock up The Lady of Shalott on an island, in a stream? Because vampires can't cross running water. Why did they carve a crucifix and a skull on the stones outside? The words said, God save us from the pestilence within these walls. They didn't mean the Black Death... they meant her! The Lady of Shalott, Lamia, she was the pestilence!"

Mark sat down. "So?" he asked Katie, at last. "What do you think we ought to do?"

"Let's draw the curtains," she said. "Let's shut out all the daylight. If you sit here, perhaps she'll be tempted to come out again. After all, she's been seven hundred years without fresh blood, hasn't she? She must be thirsty. "

Mark stared at her. "You're having a laugh, aren't you? You want me to sit here in the dark, hoping that some mythical woman is going to step out of a dirty old mirror and try to suck all the blood out of me?"

"It will prove what happened to Nigel, won't it? It will prove that the Lady of Shallot was real! Especially if we can stop her from going back into the mirror."

"Katie, this is nonsense." But Nigel was lying on the couch, silently shouting at the ceiling. And there was so much blood, and so many footprints.

Katie raised both hands in surrender. "If you think I'm being ridiculous, let's forget it. Let's call the police and tell them exactly what happened. I'm sure that forensics will prove that we didn't kill him."

Mark stood up again and went over to the mirror. He peered into the polished circle, but all he could see was his own face, dimly haloed. Nigel's death had shaken him to the core; and he had a terrible cold suspicion that Katie might be right, and that something had emerged from the mirror. But if he didn't encourage it to come out, how was he going to explain Nigel's body, to the police? And what was he going to do with the mirror?

"Okay then," he said, still staring at his own reflection. "You're the Camelot expert. If that's what you want to do, let's do it."

Katie drew the brown velvet curtains and tucked them in at the bottom to keep out the tiniest chink of daylight. It was well past eight o'clock now, but it was still pouring with rain outside and the morning was so gloomy that she need hardly have bothered. Mark pulled one of the armchairs up in front of the mirror and sat facing it.

"I feel like one of those goats they tie up, to catch tigers."

"Well, I wouldn't worry. I'm probably wrong."

Mark took out a crumpled Kleenex and blew his nose, and then sniffed, and said, "God."

"That's the blood," said Katie. Adding, after a moment, "My uncle used to be a butcher. He always said that bad blood is the worst smell in the world."

They sat in silence for a while. The smell of blood seemed to be steadily growing thicker, and riper, so that Mark could actually taste it. His throat was dry, too, and he wished he had drunk some orange juice before starting this vigil.

"You couldn't fetch me a drink, could you?" he asked Katie.

"Ssh," said Katie. "I think I can see something."

"What? Where?"

"Look at the mirror, in the middle. Like a very faint light."

Mark stared toward the mirror in the darkness. At first he couldn't see anything but overwhelming blackness. But then he saw a flicker, like somebody waving a white scarf, and then another.

Very gradually, a face began to appear in the polished circle. Mark felt a slow crawling sensation down his back, and his lower jaw began to judder so much that he had to clench his teeth to stop it. The face was pale and bland but strangely beautiful, and it was staring straight at him, unblinking, and smiling. It looked more like the face of a marble statue than a human being. Mark tried to look away, but he couldn't. Every time he turned his head toward Katie he was compelled to turn back again.

The darkened living-room seemed to grow even more airless and suffocating, and when he said, "Katie... can you see her?" his voice was muffled, as if he had a pillow over his face.

Soundlessly, the pale woman took one step out of the surface of the mirror. She was naked, and her skin was the colour of the moon. The black tarnish clung to her for a moment, like oily cobwebs, but as she took another step forward they slid away from her, leaving her luminous and pristine.