The green line on the screen was no longer straight, it was suddenly curving up and down like a slithering snake, undulating like ocean waves, moving from one side of the device to the other. Beneath the curves, a sequence of numbers began to appear, one after another. One for each of the calibrations Gregor had entered into the machine based on the etching. A mathematical code for the noise coming from the bell. Adrian’s face flushed as he looked from the curve to the numbers, hardly believing that it was working, that Gregor had been right, that Revere in the engraving had been using the glasses to measure the bell—when suddenly he noticed something.

The numbers were wrong. They didn’t match the numbers in Revere’s engraving.

Either Gregor had miscalculated, which seemed unlikely, given the man’s background and ability. Or the numbers were wrong because this wasn’t the sound that Revere had been measuring in the engraving. This wasn’t the sound—the tone Revere had been chasing, the powerful, world-changing tone—because this wasn’t the bell.

But that didn’t seem possible. The date on the engraving was 1814. Revere had made this bell in 1814, or around then, just a couple of years before he’d died. He’d made three hundred bells, worked obsessively building them up until his death. The King’s Chapel bell wasn’t just supposed to be the sweetest bell Revere had ever made. It was supposed to be his last.

“But it wasn’t,” Adrian suddenly said. “It wasn’t his last bell.”

The bell slowed in its frame, the sound receding just enough so that he could be heard. “The textbooks are wrong.”

Bevil looked at him, hands still on the heavy rope.

“That’s not true. The King’s Chapel bell was Revere’s last. It’s right in the brochures we give out downstairs.”

Adrian shook his head. With Charles’s death, he was now the singular, preeminent Revere scholar in the nation. He hadn’t realized it before—but if Charles’s thesis was right, and the engravings he’d found were authentic—there had to be another bell.

Adrian had a sudden thought. Balancing the spectrum analyzer in one hand, he reached into his pocket with the other, and his fingers felt stiff cardboard. Slowly, he pulled the coaster from the Warren Tavern free, and then gazed down at the picture emblazoned across its surface.

“What’s this all about, Professor?” Bevil asked. “What were you trying to measure with that device?”

Gregor had asked something similar, back in his lab. What was Revere up to, with those glasses? What was so important about that bell in the picture, and the sound it was supposed to have made?