Frère Sébastien stopped at the door to the porter’s room.

“Would you mind, mon frère,” the Dominican asked, suddenly formal, almost grave, “if I looked at your Book of Chants?”

It was not, Gamache knew, how the Inquisition of the past would have handled it. They’d have simply taken the book, and probably burned the young monk who had it in his possession.

Frère Luc stepped aside.

And the hound of the Lord took the last few steps in a journey that had begun hundreds of years and thousands of miles earlier. By brothers long dead.

He stepped into the dreary little room and looked at the large, plain bound book on the desk. His hand hovered over the cover and then he opened it and took a deep breath in.

Then a deep breath out.

A long, slow sigh.

“This is it.”

“How do you know?” Gamache asked.

“Because of this.” The monk picked up the book and held it in his arms.

Gamache put on his reading glasses and leaned over. Frère Sébastien was pointing to the very first word on the very first page. Above it was a neume. But where the finger was there was nothing, except a dot.

“That?” asked Gamache, also pointing. “That dot?”

“That dot,” said Frère Sébastien. There was a look of awe, of astonishment on his face. “This is it. The very first book of Gregorian chant. And this,” he lifted his finger a fraction, “is the very first musical note. It must’ve somehow come into the possession of Gilbert of Sempringham, in the twelfth century,” said the Dominican, speaking to the page and not the men around him. “Maybe as a gift, a thank-you from the Church, for his loyalty to Thomas à Becket. But Gilbert couldn’t have known how valuable it was. No one would, at the time. They couldn’t have known it was unique. Or would become unique.”

“But what makes it unique?” asked Gamache.

“That dot. It’s not a dot.”

“What is it?” It looked like a dot to Gamache. He’d rarely felt so stupid as he had since arriving in Saint-Gilbert.

“It’s the key.” Both men looked at the young portier who’d just spoken. “The starting point.”

“You knew?” Frère Sébastien asked Frère Luc.

“Not at first,” admitted Luc. “I just knew the chants here are different than any I’d ever heard or sung. But I didn’t know why. Then Frère Mathieu told me.”

“Did he know this book is priceless?” asked the Dominican.

“I don’t think he thought in those terms. But I think he knew it was unique. He knew enough about Gregorian chant to realize none of the others, in all the literature and collections, had that dot. And he knew what it meant.”

“What does it mean?” asked Gamache.

“That dot is the musical Rosetta stone,” said Frère Sébastien, then he turned to Luc. “You called it the key and that’s exactly what it is. All the other Gregorian chants are close. It’s like getting to this monastery but not being able to get in the door. The best you can do is wander around the outside. Close. But not quite there. This,” he nodded down at the page, “is the key that unlocks the door that gets us inside the chants. That gets us inside the minds and the voices of the earliest of monks. With this, we know what the original chants really sounded like. What the voice of God really sounds like.”

“How?” asked Gamache, trying not to sound exasperated.

“You tell him,” Frère Sébastien invited the young Gilbertine. “It’s your book.”

Frère Luc flushed with pride and looked at the Dominican with something close to adoration. For not only including him in this conversation, but treating him as an equal.

“It’s not just a dot.” Frère Luc turned to Gamache. “If you found a treasure map that had all the directions, but not the place to begin, it’d be useless. The dot is the starting point. It tells us what the first note should be.”

Gamache looked back down at the book, open in Frère Sébastien’s arms.

“But I thought the neume told us that,” he said, pointing to the first squiggle above the first faded word.

“No,” said Luc. Patient now. A born teacher, when working with something he knew and loved. “It only tells us to raise our voices. But from where? This dot is in the middle of the letter. The voice should start in the middle register, and go up.”