Adrian looked up from the book, his mind spinning through what he had just read. Hailey was staring at him, her backpack still over her shoulder; Nick seemed more interested in the flashier items in the exhibit case than the red-covered book.

Adrian was still digesting it all himself, but he could see from the wild look in Hailey’s eyes that she wasn’t going to wait for him to work everything through on his own. After a beat, he pointed to her backpack, then beckoned with a hand.

She glanced at Nick, but he was still occupied by the case. Then she unzipped the pack, and removed the eagle, unwrapping its body from the checkered blanket. Carefully, she handed it to Adrian, who held it gingerly, feeling the cold surface of the bronze against his fingers.

“This was never supposed to actually exist. It wasn’t even really a mold—”

“But it does exist. The eagle—”

“Not the eagle,” Adrian said, shaking his head. “The eagle’s wings.”

Adrian turned the eagle over in his hands, showing her one extended wing. He ran a finger over the curves.

Hailey seemed to understand.

“The mathematical equation,” she said, “hidden in the shape of that wing.”

Adrian nodded.

“Alchemical, occult, I wouldn’t begin to hypothesize—but obviously an equation Revere deemed to be valuable and powerful, so important that he went to great lengths to hide it.”

Hailey was watching his fingers move across the curves of the wing.

“Powerful—and incredibly complex. It would take years to solve it from the topography of such an object. Perhaps you’d even need the use of a supercomputer. And even then—it might not be possible. Certainly, Thomire didn’t know how to solve it—but by making the eagle he did manage to preserve it. But that book—”

Adrian shook his head.

“The solution isn’t written in a book. This wing is hiding an equation for a pattern of sound waves. A tone, made by the ringing of a bell.”

Hailey opened her eyes wide. But then she nodded, impressed.

“Sound waves. The curves of the eagle’s wing represent precise sound waves. It’s theoretically possible. Sound waves can affect materials at a molecular level. Everyone knows the right frequency of sound can shatter glass. But using sound for something like this, to generate the perfectly precise tone to transform molecules—that would be one hell of a bell.”

This finally caught Nick’s attention—as he pointed at the necklace in the case in front of Adrian.

“Like that bell?”

Adrian looked down, realizing that in fact the gold-looking ornament on the end of the necklace was indeed a small bell, about twice the size of an acorn. He shook his head, annoyed.

“Don’t be foolish. That bell is a trinket. Revere originally made it for a child’s dollhouse, then put it on a necklace.”

“Well, then which bell?” the man grunted.