“Oh God,” whispered Karlsson, beneath the deafening racket. “Oh Jesus. Oh God.”

Matt ran forward, his only thought that he had to stop this, had to do something, anything to help the woman. He was reaching for the button on the wall when Turner tackled him, wrapping his arms round his waist and driving him to the ground. His teeth came together on his tongue with an audible clunk and Matt tasted blood. He howled, partly in pain and partly from dreadful, guilty misery.

“No!” shouted Turner. “It’s not safe!”

“WE HAVE TO DO SOMETHING!” he screamed.

Matt was dragged to his feet. Arms wrapped round him from behind, pinning his own to his sides and holding him tightly in place.

“There’s nothing we can do,” said Turner, his voice low. “We just have to wait for it to end.”

Matt stared through the window with tears in his eyes. The woman was jerking back and forth, screeching and scratching at her skin, as though she was covered with bugs that only she could see. Her eyes were flaring crimson, and her fangs were sliding in and out, gleaming wetly under the fluorescent light. She spun into the rear wall, and Matt’s stomach lurched as her arm broke with a thick crunch; her elbow was bent back the wrong way and pointed ends of bone were sticking through the skin.

The woman jerked back into the middle of the room and hung in the air, her incoherent ranting and raving stopping as suddenly as if someone had flicked a switch. The veins stood out in her neck, and her back arched alarmingly; any further, and Matt was sure her spine would break. Her throat convulsed, as her limbs vibrated in a blur and her eyes blazed black. A howl rose from the woman’s mouth, a terrible cry that sounded like it was coming from the deepest depths of her soul. Then she went limp, and dropped to the ground like a stone.

“Open the door,” said the doctor. “Open it now, for God’s sake.”

Karlsson looked round, his eyes wide and staring, but didn’t move. Matt felt Turner’s grip on him loosen; he broke free and hammered the button beside the door. The doctor ran under the rising plastic window and slid to his knees beside the woman, his fingers pressed against her neck. For a long moment, there was silence in the wide laboratory, full of the terrible prospect of tragedy.

“She’s breathing,” said the doctor.

Matt let out a gasp of relief. Beside him, Karlsson put his hands on his knees and bent over. Matt was suddenly sure his boss was going to throw up; he was visibly swaying, and his skin had turned pale green. But Karlsson took a series of deep breaths and straightened unsteadily back up, his face a mask of shock. The Professor was a scientist, a theorist, and Matt doubted he had ever seen anything remotely as horrible as the events of the last five minutes.

“I need to get her back on the stretcher,” said the doctor. “Can one of you help me lift her?”

“Neither of you move,” said Turner. “Doctor, come out of there. Now.”

Matt turned to the Director, a deep frown on his face. Karlsson was still staring at the woman, seemingly paralysed by what he had seen.

“She needs to go to the infirmary,” said the doctor. “I need to set her arm immediately.”

“I understand that,” said Turner. “But I want to make sure this is over, and I’d like to have that window between her and us if it isn’t. So come out of there. That’s an order.”

The doctor stared at Turner, then got to his feet and walked out of the room. He pressed the button to lower the plastic barrier, and lined up beside his colleagues. Matt watched the woman’s chest rising and falling, and was surprised at the intensity of the relief that was pulsing through him. He had been sure he could handle the test, that the scientist in him would be able to rationalise it away as being for the greater good, but the reality had been almost too much to bear.

“Was that what you were expecting?” asked Turner.

Professor Karlsson shook his head. “No,” he said. “I don’t think anybody was expecting that.”

“So?” said Turner.

“So what?”

“Did it work?” asked the Director, turning to face the Professor.

“I have absolutely no idea,” said Karlsson. “Doctor?”

The doctor shrugged. “Her pulse is steady,” he said. “But if you’re asking me if she’s still a vampire, I won’t know until she wakes up or I shine a UV light on her.”

“Could you do that?” asked Turner.

The doctor narrowed his eyes. “I could,” he said. “But I really hope you’re not asking me to.”

Matt was watching the exchange when something moved in the corner of his eye. He looked back in time to see the woman open her eyes and roll her head to the side. She stared directly at him, her eyes wide and unfocused.

“Hey,” he said. “She’s awake. Look.”

Turner frowned. “Is that a good sign?” he asked.

“This was the first time this procedure was carried out on a human being, sir,” said the doctor, with a noticeable edge in his voice. “None of us knows what’s a good sign, or a bad sign, or anything in between. It doesn’t matter how many times you ask.”

Turner gave the doctor a brief, narrow-eyed stare, then stepped up to the window. “Can you hear me?” he asked, in a raised voice.

“Yes,” said the woman, her voice hoarse and slightly slurred. “I can hear you.”

“How do you feel?” asked the doctor.

The woman grimaced. “My arm hurts.”

“I know,” said the doctor. “Try not to move. We’re going to fix that for you in a minute. How do you feel, apart from that?”

“I don’t know,” said the woman. “I don’t …”

“Take your time,” said the doctor.

The woman nodded. She lay on the floor, her body still, her breathing slow and deep, and closed her eyes. A long second later they flew open, and a smile of such staggering beauty broke across her face that it made Matt gasp out loud.

“It’s gone,” she said. “My God. I can’t feel it any more. It’s really gone.”

Marie Carpenter’s smile widened, and she burst into tears.

Jamie found himself distracted as he walked down the cellblock corridor, and as a result he didn’t realise his mother’s cell was empty as soon as he exited the airlock.

The reasons for his distraction were clear. For the entirety of his Blacklight career, the operational SOP had been to destroy vampires on sight, which meant that the cells on Level H were very rarely full. The fourth room on the right was occupied by Valentin, the last on the left by his mother, and that was usually all.

Now, the first room on the left contained a man lying asleep on a bed. Two cells down, a pair of middle-aged women were huddled together on plastic chairs, talking so quietly that even his supernatural hearing could barely make out their words. Halfway along the corridor on the right, a teenage boy stared petulantly at Jamie as he passed, his hands stuffed into the pockets of his jeans, his eyes full of faint red fire. And on the opposite side of the cellblock, three further cells along, he found the family he had rescued the night before.

The man was asleep on the bed, his body rolled towards the wall. The woman was sitting in a chair, gently rocking her daughter in her arms. She looked up as Jamie paused outside the cell’s UV barrier, smiled, and raised a finger to her lips in a message that was abundantly clear.

Don’t wake them up.

He smiled back, and nodded. He glanced round the rest of the cell and saw the box he had carried on the floor at the back; the cat’s black and white head peered over the cardboard lip, and Jamie was pleased to see that someone had found her a bowl of water and a plate of what looked like offcuts of ham.