It was the first symbol that was etched into the eagle.

“This is the pre-chemistry symbol for sulfur.”

“Sulfur,” Nick repeated.

“It’s one of the basic elements. You remember your periodic table?”

When Nick didn’t respond, she continued.

“It’s a very common element—the fifth most common substance by mass on earth, actually—found almost everywhere in nature. Historically, very important, because it has a lot of unique properties. For instance, it’s very flammable; in the Bible, it’s what they mean when they refer to ‘brimstone.’”

“And this symbol, on the eagle—it means something to you?”

Hailey began flipping yellowing pages again.

“Not on its own. But that second symbol—”

She stopped on another page in the old manuscript. Another table of images; halfway down, Nick spotted the curved second symbol, which seemed more familiar than the first.

“Libra,” Hailey said. “It’s an astrological sign. On the Zodiac it’s supposed to represent a balanced scale.”

Nick had been in plenty of courthouses up and down the commonwealth; he’d seen more than his fair share of statues meant to represent that particular astrological sign.

“Scales of justice,” Nick said.

“But here, it also means something else.”

She had her finger on the text next to the picture in her book.

Sublimation.

“You might have learned the term in chemistry. OK, maybe you didn’t. But it’s when something solid dissolves directly into a gaseous state. The way dry ice goes straight from being a solid to a gas, without turning into liquid water in between. It was an important pre-chemistry lab technique.”

Nick turned from the book to the two symbols on the eagle. They were so small, so seemingly inconsequential, he was amazed Hailey had even noticed them, let alone guessed at what they might mean. Even so, he was still completely in the dark. But Hailey was gripped by something, now. As he watched, she rummaged beneath the workbench and came back with two pairs of clear safety goggles.

She handed one pair to Nick, while donning the other. Nick looked at the glasses with suspicion, but Hailey wasn’t slowing down to explain.

She held out a hand, nodding toward Nick’s front pants pocket, where he had her flask, now filled with battery acid from the Ford Taurus outside. Once he’d handed it over, she carefully opened the diary from Gail’s trunk to the first page, revealing the slim sheet of copper, which flashed in the fluorescent light.

“The thing about solving really difficult puzzles,” she said, as she carefully opened the top of the flask, “is that it’s all about context. These two symbols on their own don’t really mean much. But when you put them together—and look at the context—things begin to connect.”

She held the flask above the copper page, then glanced at Nick, who was finally securing his own safety goggles over his eyes.