But Dr. Brunel’s game of choice, his drug of choice, was computers. He was a cyber junkie, and Gamache had brought him uncut heroin in the form of this gnarly puzzle.

“I’ve never seen so many layers of security,” said Jérôme. “Someone’s tried very hard to hide this thing.”

“What thing, though?” Gamache asked.

“You asked us to find out who really leaked that video of the raid on the factory,” Superintendent Brunel said. “The one you led, Armand.”

He nodded. The video was taken from the tiny cameras each of the agents wore, attached to their headphones. They recorded everything.

“There was an investigation, of course,” Superintendent Brunel continued. “The conclusion of the Cyber Crimes division was that a hacker had gotten lucky, found the files, edited them, and put them on the Internet.”

“Bullshit,” said Dr. Brunel. “A hacker could never have just stumbled on those files. They’re too well guarded.”

“So?” Gamache turned to Jérôme. “Who did?”

But they all knew who’d done it. If not a lucky hacker, it had to be someone inside the Sûreté, and high enough up to cover his trail. But Dr. Brunel had found that trail, and followed it.

They all knew it would lead to the office right above them. To the very highest level in the Sûreté.

But Gamache had long since begun to wonder if they were asking the right question. Not who, but why. He suspected they’d find that the video was simply the disgusting dropping of a much larger creature. They’d mistaken the merde for the actual menace.

Armand Gamache looked at the gathering. A senior Sûreté officer, past her retirement age. A rotund doctor. And himself. A middle-aged, marginalized officer.

Just the three of them. And the creature they sought seemed to grow each time they caught a glimpse of it.

Gamache knew, though, that what was a disadvantage was also an advantage. They were easily overlooked, dismissed, especially by people who believed themselves invisible and invincible.

“I think we’re getting closer, Armand, but I keep hitting dead ends,” said Jérôme. The doctor suddenly looked a little furtive.

“Go on,” said Gamache.

“I’m not certain, but I think I detected a watcher.”

Gamache said nothing. He knew what a watcher was, in physical as well as cyber terms. But he wanted Jérôme to be more precise.

“If I have, he’s very cunning and very skilled. It’s possible he’s been watching me for a while.”

Gamache rested his elbows on his knees, clasping his large hands in front of him. Like a battleship plowing toward its target.

“Is it Francoeur?” Gamache asked. No need to pretend otherwise.

“Not him personally,” said Jérôme, “but I think whoever it is is within the Sûreté network. I’ve been doing this for a long time now, and I’ve never seen anything this sophisticated. Whenever I stop and look, he fades into the background.”

“How do you even know he’s there?” asked Gamache.

“I don’t for sure, but it’s a sense, a movement, a shift.”

Brunel paused and for the first time Gamache saw in the cheerful doctor a hint of concern. A sense that as good as he was, Dr. Brunel might be up against someone better.

Gamache sat back in his chair as though something had walked by him, and pushed. What have we uncovered?

Not only were they hunting the creature, it seemed the creature might now be hunting them.

“Does this watcher know who you are?” he asked Jérôme.

“I don’t think so.”

“Think?” asked Gamache, his voice sharp, his eyes hard.

“No,” Jérôme shook his head. “He doesn’t know.”

Yet. The word was unspoken, but implied. Yet.

“Be careful, Jérôme,” said Gamache, as he rose and picked up Henri’s leash. He said his good-byes, left them, and headed into the night.

The lights of the cities and towns and villages faded in his rearview mirror as they drove deeper into the forest. After a while the darkness was complete, except for the beams of his headlights on the snowy roads. Eventually he saw a soft glow ahead, and knew what it was. Gamache’s car crested a hill, and there in the valley he saw three huge pines lit with green and red and yellow Christmas lights. Thousands of them, it seemed. And around the village cheery lights were hung along porches and picket fences and over the stone bridge.