On the TV screen the helicopter camera zoomed tight on a group of low bushes. There were uniformed cops standing around, and police tape, and a suggestion of a half-concealed figure on the ground, black shoes and black pant legs, under leafy branches. The ticker still said Shooting Victim Found in Park.

Reacher asked, “What exactly did McCann want to understand?”

The old lady said, “He wanted to know why some web sites can’t be found. Which was fundamentally a question about search engines. His image of the swimming pool became useful. He imagined millions of tennis balls, some bobbing up on the water, some trapped deeper down by the weight of the others. So I asked him to imagine a search engine as a long silk ribbon, being pulled up and down and in and out, weaving through the balls every which way, sliding over their wet fuzzy surfaces at tremendous speed. And then to imagine that some balls had been adapted, to have spikes instead of fuzz, like fish hooks, and that other balls had been adapted to have no fuzz at all, to be completely smooth, like billiard balls. Where would the silk ribbon snag? On the spikes, of course. It would slide over the billiard balls completely. That’s what Peter needed to understand about search engines. It’s a two-way street. A web site must want to be found. It must work hard to develop effective spikes. People call it search engine optimization. It’s a very important discipline now. That said, it’s equally hard work to be a billiard ball. Staying secret isn’t easy either.”

Chang said, “Secret web sites imply illegality.”

“Indeed,” the old lady said. “Or immorality, I suppose. Or both at once. I’m naïve about such things, but one imagines pornography of the most unpleasant sort, or mail-order cocaine, and so forth. It’s called the Deep Web. All those smooth billiard balls. Millions of them. No spikes, no hooks, nothing but going about their business with no one watching. The Deep Web might be ten times bigger than the Surface Web. Or a hundred. Or more. No one knows. How could they? Not to be confused with the Dark Web, of course, which is merely out-of-date sites with broken links, like dead satellites whirling through space forever. Which makes the Dark Web more like ancient archaeology, and the Deep Web more like the wrong side of the tracks. Not that either one is actually dark or deep or either side of any actual tracks, you understand. The internet is not a physical place. There are no physical characteristics to it at all.”

On the TV screen an ambulance rolled into the overhead shot, slowly over the grass, lights flashing forlornly, being followed by what looked like a coroner’s wagon. People got out, and joined the cops.

Chang asked, “So how can a person find secret web sites?”

“A person can’t,” the old lady said. “Not from the outside, anyway. You can’t use a search engine, because the sites are smooth. You need the exact address. Not just CoffeeShop.com, but something like CoffeeShop123xyz.com. Or much worse, of course, in reality. A unique resource locator combined with a super-secure password, all rolled into one. Apparently such addresses circulate through certain communities by word of mouth.”

On the TV screen a dark blue Crown Vic bumped over the grass and parked. Two men in suits climbed out. Detectives, presumably. The ticker changed to Lincoln Park Homicide. Reacher could hear more helicopters in the air, about a mile away. Rival channels, late to the party.

He asked, “Did McCann tell you what kind of a web site he was looking for?”

The old lady said, “No.”

On the screen men squatted by the black-clad figure on the grass. Detectives and the medical examiner, Reacher supposed. He knew the drill. He had squatted by horizontal figures many times. Some had been alive. This one wasn’t, he knew. There was no urgency. No hustle. No shouting voices. No backboards, no IV lines, no breathing tubes, no chest compressions.

Lincoln Park Homicide.

The old lady said, “That’s Peter, isn’t it? Why else would you be asking me about him? Why else would the FBI be interested in me?”

Chang didn’t answer either question, and Reacher said nothing, because as the old lady spoke the TV picture changed. To a house. An undistinguished brownstone, on an undistinguished street. Peter McCann’s brownstone. The old lady’s house. Where they had been, moments before. It was recognizable. It was familiar. The front of it was all lit up by flashing red lights. Cops were running up the stoop.

Much too soon for a connection to have been made. The cops in the park hadn’t even looked in McCann’s pockets yet. They hadn’t found a wallet, hadn’t checked the driver’s license, didn’t know who he was, and didn’t know where he lived. They were still waiting for the all-clear from the medical examiner. Reacher knew how it worked. He had sat back on his heels many times, just waiting. Death had to be pronounced, before the body became evidence.

Not yet connected. A separate investigation. The ticker changed to Anti-Terror Cops Storm Chicago Dwelling.

Reacher turned back to the old lady and asked, “Did you call 911?”

The old lady said, “Yes, I did.”

“When?”

“As soon as I closed my door on you.”

“Why?”

“I didn’t like the look of you.”

“Neither one of us?”

“You especially. You don’t look like what you say you are. Not like an FBI agent on the television.”

“I was undercover. Pretending to be a bad guy.”

“Your act was convincing.”

“So you called 911.”

“Immediately.”

“What did you say?”

“I had armed terrorists in my house.”

“Why that?”

“This is Chicago. That’s the only way to get a response in less than four hours.”

Chang said, “We should probably get going.”

Reacher said, “No, let’s stay a little longer. Five more minutes can’t hurt.”

They got refills of coffee, and the old lady wanted more cake, so Reacher and Chang got more too, to keep her company. The TV changed to a split screen, with the park on the left, and the house on the right, over individual labels saying Lincoln Park Homicide and Terror Alert, both of those labels centered over the main ticker, which said Busy Day for Cops.

The second cup of coffee was as good as the first. As was the cake. A body bag showed up in the park, and an ambulance arrived at the house. The body bag was zipped up and carried to the coroner’s wagon, and EMTs came out of the ambulance and ran up the stoop and in the house. Later they came out again with an injured man on a gurney. Hackett, presumably, although it was hard to be sure. The guy’s face was bandaged from the neck up, like an Egyptian mummy, and his clothes were covered with a sheet.

Then like a slow-burn visual effect in a movie the cops drove out of the park, and four long minutes later they showed up at the house, in the same cars, all the way from the left of the screen to the right, a short electronic hop but a circuitous real-world route. The same detectives got out and rushed up the stoop and went inside the house, and a minute later they came back out again, talking urgently on their cell phones.

The ticker changed to Official Says Cases Are Connected.

Reacher said, “Ma’am, I’m very sorry for your loss, and I’m very sorry for the intrusion you’re about to suffer. The Chicago PD will want to ask you questions. And it’s not like it is in the television shows. The FBI can’t come in and take over their case. We have to leave them alone. So we’d appreciate it if you don’t even tell them we’ve talked. There are all kinds of sensitivities there. Better not to tell them about us at all. Even about us being at the house earlier. They don’t need to know we beat them to it.”

“Are you asking me to lie to them?”

“I will, if they ask me who told them terrorists, and why.”