‘Enlighten me.’

‘People know this guy is using the underground to get close to his victims. They’re afraid that if they say they saw anything, he’ll get them in their bathroom or laundry room or garage.’

Rhyme couldn’t argue with that attitude. What could be more frightening than to think you were alone and safe in the lower levels of your home or office or a public building and learn that you weren’t alone at all; you had lethal company. Like a moist, venomous centipede uncurling under the blankets of your bed as you slept.

Sachs had brought Braden Alexander’s clothing too. Cooper went through each item carefully but the water had eradicated all trace – if there’d been any in the first place, which was unlikely, Sachs said, because the contact between the two men had been minimal. The handcuffs revealed no trace and, like the others, were generic.

Cooper ran other samples of swabs from the implant bag. Most were negative. But finally he had a hit. Reading from the computer screen, he said, ‘Hypochlorous acid.’

Rhyme looked over the mass spectrum. ‘Curious. It’s pure. Not diluted.’

‘Right.’ Cooper reached under the face shield and shoved his glasses higher on his nose. Rhyme wondered, as he often did, why he didn’t get frames that fit.

Hypochlorous acid – a form of chlorine – was added to New York City drinking water, as in most cities, for purification. But because this sample was undiluted, it had not come from the flood that had destroyed the Belvedere parking garage crime scene. This was the form of the chemical in its pure state, before it was added to the water system.

Rhyme said, musing, ‘It’s a weak acid. At higher levels, I suppose, it could be deadly, though. Or maybe he just picked it up because he was near one of the boxes that dispense it into the water supply. Sachs, at the first or second scenes, in the tunnels? There were water pipes, right?’

‘Water and, in one, sewage.’

‘Incoming and outgoing,’ joked Pulaski. Drawing laughs. From everyone except Rhyme.

‘Any other pipes – maybe some feeding chlorine into the mains?’

‘I don’t remember.’

‘I want to find out. If this chlorine is from tap water purification it’s not helpful. If it’s from a poison he’s planning to use, then we can start checking sources.’ Rhyme called up the pictures from the first two crime scenes. ‘Let’s get somebody back to the scenes and find out if there’s a feeder line for the chemical.’

Sachs asked, ‘Do you want Crime Scene to search?’

‘No, just a uniform’ll be fine,’ Rhyme said. ‘Anybody. But soon. Now .’

Sachs called Dispatch and had patrol cars sent to each of the two previous crime scenes, with instructions on what to look for.

Twenty minutes later Sachs’s phone rang. She answered, then hit speaker.

‘Okay, Officer, you’re on with me and Lincoln Rhyme.’

‘I’m at the Elizabeth Street scene, Detective. The Chloe Moore homicide.’

‘Where are you exactly?’ Rhyme asked.

‘In the tunnel, next to the crime scene lamps and battery packs.’

Rhyme told him, ‘I need you to look for any pipes or reservoirs marked “hypochlorous acid”, “chlorine” or the letters “Cl”. They’d have a hazard diamond on them and probably a skin and eye irritant warning.’

‘Yes, sir. I’ll do that.’

The patrolman kept up a narrative as he walked from the place where the body’d been found, near the claustrophobia tunnel, to the bricked off wall a hundred yards away.

Finally: ‘Nothing, sir. Only markings are DS  and DEP  stamped on the pipes.’ Department of Sanitation and Department of Environmental Protection, which was the agency overseeing the New York City water supply.

‘And some kind of boxes marked IFON  – don’t know what that is. But nothing about chemicals.’

Sachs thanked him and disconnected.

Soon a member of the other team called in, from underneath the Provence2 crime scene – the slaughterhouse octagon, where Samantha Levine had died.

This officer reported the same. No DEP systems for introducing hypochlorous acid into the water system.

After disconnecting, Rhyme said, ‘So, it’s probably got some connection with the unsub. Let’s find out where somebody would buy it, or how it’s made. Ron?’

But a search revealed what Rhyme suspected: There were dozens of chemical supply companies in the tri state area. And the unsub would have bought a small amount, so he’d use cash. He might even have stolen a can or two. A useless lead.

Rhyme wheeled forward to the examination table, staring at the implants, his mind considering the implications of the numbers.

1 7 t h

‘We have “the second”, “forty” and “seventeenth”. What the hell is he saying?’ Rhyme shook his head. ‘I still like the idea he’s sending us someplace. But where?’

Sachs said, ‘No scalloped border, like the others.’

But TT Gordon pointed out, ‘That was scarification, remember? If he was going to include them he would have used the same scalpel that he used to cut the incisions for the implants. He would’ve done that later, after he’d placed the implant. From what I heard, sounds like you interrupted him before he could get very far.’

‘Well, he escaped  before he got very far,’ Sachs muttered.

Pulaski added, ‘No “the” with the seventeenth.’

‘Maybe that’s exactly how the quote goes, whatever that quote is.’

‘Implants take time, too,’ Gordon noted.

‘Good point. He’d want to move fast.’ Rhyme nodded toward the tattoo artist. ‘“The” might have been too much.’

Everyone’s eyes were on the numbers.

What the hell was the unsub’s message? What could he possibly be wanting to say to us, to the city, to the world?

If his model was the Bone Collector, as it seemed to be, that message was about revenge most likely. But for what? What did ‘the second’, ‘forty’, and now ‘17th’ say about a wrong he wanted vindicated?

That you could also dub Unsub 11 5 the Skin Collector wasn’t enough for Rhyme. There was more to his purpose, he sensed, than being a legacy of a psychotic killer stalking the streets of New York more than a decade ago.

TT Gordon broke the silence, ‘Anything else you need me for?’

‘No,’ Rhyme said. ‘Thanks for your help. Appreciate it.’

Drawing a raised eyebrow from Amelia Sachs. Civility was not a Lincoln Rhyme quality. But he found he was enjoying the company of this man with elaborate facial hair and a command of Strunk and White’s The Elements of Style .

Gordon pulled his tuxedo jacket on. Again, Rhyme thought, it seemed too thin for such a slight frame on a foul, gray day like this one. ‘Good luck.’ He paused in front of Rhyme, looking him over. ‘Hey, looks like you’re one of us, dude.’

Rhyme looked up. ‘One of who?’

‘You’re modded.’

‘How’s that?’

He pointed to Rhyme’s arm, where scars were prominent, from the surgery to restore motion to his right arm and hand. ‘Looks like Mount Everest, those scars there. Upside down to you.’

True, curiously, the triangular pattern did look like the famous mountain.

‘You want me to fill it in, just let me know. Or I could do something else. Oh, dude, I know. I could add a bird.’ He nodded toward the window. ‘One of those hawks or whatever they are. Flying over the mountains.’

Rhyme laughed. What a crazy thought. Then his eyes strayed to the peregrine falcons. There was  something intriguing about the idea.

‘Trauma to the skin is contraindicated for someone in his condition.’ Thom was in the doorway, arms crossed.

Gordon nodded. ‘Guess that means no.’

‘No.’

He looked around the room. ‘Well, anybody else?’

‘My mother would kill me,’ near middle aged Mel Cooper said.

‘My wife,’ Pulaski said.

Amelia Sachs only shook her head.

Thom said, ‘I’ll stick with the one I have.’

‘What?’ Sachs asked, laughing. But the aide said nothing more.