It was Lynley’s decision. He decided to hold off making it. He said, “I want to think about this,” and to Winston, “Tell Crimewatch we may have something for them, but we’re working on it.”

Nkata looked uneasy, but he went for the phone. Stewart looked pleased as he returned to his desk.

Lynley nodded to Havers, an I’ll-see-you-now look. She grabbed up what looked like a pristine notebook and followed him out of the incident room.

“Good work,” he told her. He noted that she’d even dressed more suitably today, in a tweed suit and brogues. The suit had a stain on the skirt and the brogues weren’t polished, but it was otherwise a remarkable change in a woman who usually favoured drawstring trousers and T-shirts bearing groan-inducing puns.

She shrugged. “I’m capable of taking the hint when I’m clubbed with it, sir.”

“I’m glad to hear that. Get your things and come with me.”

Her face altered, its hopeful brightness betraying her even as it deeply touched him. He wanted to tell her not to wear her professional heart on her sleeve, but he held his tongue. Havers was who Havers was.

SHE DIDN’T ASK where they were going till they were in the Bentley and heading in the direction of Vaux-hall Bridge Road. Then she said, “Are we doing a runner, sir?”

He said, “Believe me, I’ve thought about it more than once. But Webberly tells me there’s a route to dealing with Hillier. I’ve just not discovered it yet.”

“That must be like searching for the Holy Grail.” She examined her brogues and appeared to note their sad condition. She wet her fingers on her tongue and rubbed the damp against a scuff, without result. She said, “How is he, then?”

“Webberly? Slow progress, but progress.”

“Well, that’s good, isn’t it?”

“Everything but the slow part. We need him back before Hillier self-destructs and takes us all down with him.”

“D’you think it’ll come to that?”

“Sometimes,” he said, “I don’t know what to think.”

At their destination, parking was its usual nightmare. He squeezed the Bentley in front of the entrance to the Kings Head and Eight Bells pub, directly beneath a “Do NOT Block This Entrance” sign, to which “You Will Die If You Do” had been added. Havers raised her eyebrow.

“What’s life without risk?” Lynley asked. But he put a police placard prominently on the dashboard.

“Now that’s living dangerously,” Havers noted.

They walked the few yards up Cheyne Row to the house at the corner of Lordship Place, where they found St. James being regaled by both Deborah and Helen, who were leafing through magazines as they chatted about “The absolute solution to everything. Simon, you’ve married a genius.” They were all in the lab.

“Logic,” Deborah replied. “It was nothing more.” She looked up and saw Lynley and Havers in the doorway. She said, “Just in time. Look who’s here. You won’t even have to go home to talk him into it, Helen.”

“Talk me into what?” Lynley went to his wife, tilting back her chin to examine her face. “You’re looking tired.”

“Don’t be a mother hen,” she chided. “You’ve got worry lines coming out on your forehead.”

“That’s down to Hillier,” Havers said. “We’ll all look ten years older in another month.”

“Isn’t he due to retire?” Deborah asked.

“Assistant commissioners don’t retire, my love,” St. James told his wife. “Not until the last hope of being made commissioner is finally beaten out of them.” He looked at Lynley. “I take it that doesn’t seem likely to happen soon?”

“You take it correctly. Have you got anything for us, Simon?”

“I expect you mean information and not whisky,” St. James said. He added, “Fu.”

“Phoo?” Havers said. “As in…what? Phooey? Typhoo tea?”

“As in the letters F and U.” On a china board, St. James had been working on a diagram with splotches of faux blood, but he left it and went to his desk where he took from the top drawer a paper on which was drawn the same symbol that had been on the bottom of the note they’d received at the Yard, purporting to be from the serial killer. “It’s a Chinese symbol,” St. James explained. “It means authority, divine power, and the ability to judge. It stands, in fact, for justice. And it’s pronounced Fu.”

Helen said, “Is that helpful, Tommy?”

“It’s in keeping with the message of the note he sent. And to some extent, with the mark on Kimmo Thorne’s forehead as well.”

“Because it is a mark?” Havers asked.

“I expect that would be Dr. Robson’s point.”

“Even if the other mark’s from alchemy?” Deborah asked the last question of her husband.

“It’s the fact of the marking, I daresay,” St. James replied. “Two distinct symbols with interpretations readily available. Is that what you mean, Tommy?”

“Hmm. Yes.” Lynley studied the piece of paper on which the mark had been reproduced and an explanation of the mark appeared. He said, “Simon, where did you get the information?”

“Internet search,” he said. “It wasn’t difficult.”

“So our boy’s got access to a computer as well,” Havers noted.

“That narrows it down to half the population of London,” Lynley said grimly.

“I think I can eliminate at least a portion of that group. There’s something else.” St. James had moved to a worktable where he was laying out a line of photographs. Lynley and Havers joined him, while Deborah and Helen remained at the other worktable, a selection of magazines open between them.

“I had these from SO7,” St. James said, in reference to the pictures, which Lynley saw were of each of the dead boys, along with respective enlargements of one small portion of each boy’s torso. “D’you recall the autopsy reports, Tommy, how they all mention a specific area of what they called ‘woundlike bruising’ on every one of the bodies? Well, have a look at this. Deborah did the enlargements for me last night.” He reached for one of the larger photos.

Lynley examined it, Havers looking over his shoulder. In the picture, he saw the bruising that St. James was talking about. He discerned that it was actually more of a pattern than a bruise, most distinguishable on Kimmo Thorne’s body because he was the only white youth. On Kimmo, a central pale area was ringed by dark bruiselike flesh. In the centre of the pale portion of this, two small marks had the look of burns. With variations due to the pigment of each boy, this distinctive mark was the same on every successive photograph that St. James handed over. Lynley looked up once he’d seen them all.

“Did SO7 actually miss this?” he asked. What he thought was, Christ. What a bloody cock-up.

“They mention it in the autopsies. The problem was in their term of reference. Calling it a bruise.”

“What do you make of it yourself? It looks something between a bruise and a burn.”

“I had a good idea, but I wasn’t entirely sure initially. So I scanned the photos and sent them over to a colleague in the States for a second opinion.”

“Why the States?” Havers had taken up one of the pictures and had been frowning down at it, but now she looked up curiously.

“Because, like nearly anything else you might imagine as a weapon, they’re legal in America.”

“What?”

“Stun guns. I think that’s how he’s incapacitating the boys. Before he does the rest.” St. James went on to explain how the characteristics of the bruiselike wounds on the bodies compared point by point to the kind of bruise that was the result of being jolted by the fifty thousand to two hundred thousand volts of electricity that such a weapon discharged. “Each of the boys was hit in relatively the same place on the body, on the left side of the torso. That tells us that the killer’s using the gun in the same way each time.”

“If you’ve got something that works, why mess about with it,” Havers said.

“Exactly,” St. James agreed. “The electricity from the stun gun scrambles the body’s nervous system, leaving the victim-as the name implies-literally stunned, unable to move even if he wants to. His muscles work rapidly but without any efficiency. His blood sugar is converted to lactic acid, which depletes him of energy. His neurological impulses are interrupted. He’s weak, confused, and disoriented.”