Norman squinted at the image set in the door. It looked like two shields—the kind medieval knights would have carried—hanging next to each other from a tree branch. The shield on the left featured an X, while the one on the right displayed an inverted V, set with three stars. “What is it?”

“It’s a symbol taken from a colophon,” April said. “Before there were title pages in books, printers used a colophon on the back page. It was basically just a few lines explaining who worked on the book. But it also included an image, a set of symbols unique to the printer.”

“So that’s Gutenberg’s colophon?”

“No. The X is the Greek symbol chi, and the upside-down V is the Greek symbol lambda,” she said, tracing the letters with her finger in the air. “The shield on the left represented a man named Johann Fust. And the shield on the right stood for his business partner Peter Schöffer.”

“And they were . . . ?”

“Gutenberg’s associates,” April whispered. She turned away from the door toward a gate on the opposite wall. She took out a key and unlocked it. “Come on,” she said, opening the door behind the gate and entering the room beyond. She didn’t bother turning on the lights; the layout of the room was etched on her brain. She grabbed Norman by the arm. “Follow me.” She dragged him across thick carpet, past wooden tables topped with brass lamps.

Norman trailed behind April, now and then banging into the sides of benches. “The Rosenwald Room. This is your hideout, isn’t it?”

“You could call it that,” she replied.

They passed rows of bookshelves, moving toward the back wall. “Where are we going?” he asked.

April heard the door open behind them. She stopped and listened as two agents entered the room. April squeezed Norman’s arm so hard he moved to pry her fingers off. She pulled him forward, farther into the enclave of rare books. They finally reached the back corner of the room, where the last bookshelf met the wall. The two sets of feet scuttled toward them. “They’re getting closer,” Norman said in April’s ear.

She wasn’t interested. She kept her back to him, her body pointed toward a small control box on the wall next to her, its wide, digitized panel glowing a soft orange. April put her hand against it, triggering a faint click from the bookcase.

A loud thud echoed behind them. April turned. The agents were an aisle away. She felt the ground quiver with every step they took. They were running. The lit panel next to April showed them exactly what to run toward.

“Stop!” one of the agents yelled.

“Go!” Norman said, tapping rapidly on April’s shoulder. She grabbed him and fell into the bookcase. It gave way, not falling but spinning, toward the wall.