“Good meeting you both,” he said. “And thanks, M.E.”

Then he stepped out into the canvas gloom and shut the door and the agents surrounded him and walked him down the length of the tent toward the building. Reacher glimpsed uniformed Capitol security people waiting inside. Armstrong stepped through the door and it closed solidly behind him. Froelich pulled away from the curb and eased around the parked cars and headed north in the direction of Union Station.

“OK,” she said, like she was very relieved. “So far so good.”

“You took a chance there,” Reacher said.

“Two in two hundred eighty-one million,” Neagley said.

“What are you talking about?”

“Could have been one of us who sent the letters.”

Froelich smiled. “My guess is it wasn’t. What did you think of him?”

“I liked him,” Reacher said. “I really did.”

“Me too,” Neagley said. “I’ve liked him since Thursday. So now what?”

“He’s in there all day for meetings. Lunch in the dining room. We’ll take him home around seven o’clock. His wife is home. So we’ll rent them a video or something. Keep them locked up tight all evening.”

“We need intelligence,” Reacher said. “We don’t know what exact form this demonstration might take. Or where it will be. Could be anything from graffiti upward. We don’t want to let it pass us by without noticing. If it happens at all.”

Froelich nodded. “We’ll check at midnight. Assuming we get to midnight.”

“And I want Neagley to interview the cleaners again. We get what we need from them, we can put our minds at rest.”

“I’d like to do that,” Froelich said.

They dropped Neagley at the Federal lockup and then drove back to Froelich’s office. Written FBI forensic reports were in on the latest two messages. They were identical to the first two in every respect. But there was a supplementary report from a Bureau chemist. He had detected something unusual about the thumbprints.

“Squalene,” Froelich said. “You ever heard of that?”

Reacher shook his head.

“It’s an acyclic hydrocarbon. A type of oil. There are traces of it present in the thumbprints. Slightly more on the third and fourth than the first and second.”

“Prints always have oils. That’s how they get made.”

“But usually it’s regular human finger oil. This stuff is different. C-thirty-H-fifty. It’s a fish oil. Shark-liver oil, basically.”

She passed the paper across her desk. It was covered in complicated stuff about organic chemistry. Squalene was a natural oil used as an old-fashioned lubricant for delicate machinery, like clockwork watches. There was an addendum at the bottom which said that when hydrogenated, squalene with an e becomes squalane with an a.

“What’s hydrogenated?” Reacher asked.

“You add water?” Froelich said. “Like hydroelectric power?”

He shrugged and she pulled a dictionary off the shelf and flicked through to H.

“No,” she said. “It means you add extra hydrogen atoms to the molecule.”

“Well, that makes everything clear as mud. I scored pretty low in chemistry.”

“It means this guy could be a shark fisherman.”

“Or he guts fish for a living,” Reacher said. “Or he works in a fish store. Or he’s an antique watchmaker with his hands dirty from lubricating something.”

Froelich opened a drawer and flipped through a file and pulled a single sheet. Passed it across. It was a life-size fluoroscope photograph of a thumbprint.

“This our guy?” Reacher asked.

Froelich nodded. It was a very clear print. Maybe the clearest print Reacher had ever seen. All the ridges and whorls were exactly delineated. It was bold and astonishingly provocative. And it was big. Very big. The pad of the thumb measured nearly an inch and a half across. Reacher pressed his own thumb alongside it. His thumb was smaller, and he didn’t have the most delicate hands in the world.

“That’s not a watchmaker’s thumb,” Froelich said.

Reacher nodded slowly. The guy must have hands like bunches of bananas. And rough skin, to print with that degree of clarity.

“Manual worker,” he said.

“Shark fisherman,” Froelich said. “Where do they catch a lot of sharks?”

“Florida, maybe.”

“Orlando’s in Florida.”

Her phone rang. She picked it up and her face fell. She looked up at the ceiling and pressed the phone into her shoulder.

“Armstrong needs to go over to the Department of Labor,” she said. “And he wants to walk.”

It was exactly two miles from the Treasury Building to the Senate Offices and Froelich drove the whole way one-handed while she talked on her phone. The weather was gray and the traffic was heavy and the trip was slow. She parked at the mouth of the white tent on First Street and killed the motor and snapped her phone closed all at the same time.

“Can’t the Labor guys come over here?” Reacher asked.

She shook her head. “It’s a political thing. There are going to be changes over there and it’s more polite if Armstrong makes the effort himself.”

“Why does he want to walk?”

“Because he’s an outdoors type. He likes fresh air. And he’s stubborn.”

“Where does he have to go, exactly?”

She pointed due west. “Less than half a mile that way. Call it six or seven hundred yards across Capitol Plaza.”

“Did he call them or did they call him?”

“He called them. It’s going to leak so he’s trying to preempt the bad news.”

“Can you stop him going?”

“Theoretically,” she said. “But I really don’t want to. That’s not the sort of argument I want to have right now.”

Reacher turned and looked down the street behind them. Nothing there except gray weather and speeding cars on Constitution Avenue.

“So let him do it,” he said. “He called them. Nobody’s luring him out into the open. It’s not a trick.”

She glanced ahead through the windshield. Then she turned and stared past him, through his side window, down the length of the tent. Flipped her phone open and spoke to people in her office again. She used abbreviations and a torrent of jargon he couldn’t follow. Finished the call and closed her phone.

“We’ll bring a Metro traffic chopper in,” she said. “Keep it low enough to be obvious. He’ll have to pass the Armenian Embassy, so we’ll put some extra cops there. They’ll blend in. I’ll follow him in the car on D Street fifty yards behind. I want you out ahead of him with your eyes wide open.”

“When are we doing this?”

“Within ten minutes. Go up the street and left.”

“OK,” he said. She restarted the car and rolled forward so he could step onto the sidewalk clear of the tent. He got out and zipped his jacket and walked away into the cold. Up First Street and left onto C Street. There was traffic on Delaware Avenue ahead of him and beyond it he could see Capitol Plaza. There were low bare trees and open brown lawns. Paths made from crushed sandstone. A fountain in the center. A pool to the right. To the left and farther on, some kind of an obelisk memorial to somebody.

He dodged cars and ran across Delaware. Walked on into the plaza. Grit crunched under his shoes. It was very cold. His soles were thin. It felt like there were ice crystals mixed in with the crushed stone underfoot. He stopped just short of the fountain. Looked around. Perimeters were good. To the north was open ground and then a semicircle of state flags and some other monument and the bulk of Union Station. To the south was nothing except for the Capitol Building itself far away across Constitution Avenue. Ahead to the west was a building he assumed was the Department of Labor. He looped around the fountain with his eyes focused on the middle distance and saw nothing that worried him. Poor cover, no close windows. There were people in the park, but no assassin hangs around all day just in case somebody’s schedule changes unexpectedly.