“Besides gravity and motion, Newton’s most famous discoveries had to do with light. One of those discoveries was that what appears to be a uniform beam of light is actually made up of many different wavelengths.”

“The colors of a rainbow,” Nick said, surprising her.

“Correct. The thing is, historians of Newton believe that he came to this conclusion not by pure scientific experimentation, but because of his beliefs in prescientific, occult endeavors, which posited that everything in nature—from metals, to consciousness, to the universe itself—could be broken down to a handful of ‘base’ constituent parts.”

She could tell she had just lost Nick again, but it didn’t matter. He was about to see what she was heading toward for himself.

“Hold the bottle up to the light where it comes off the mirror.”

Again, he did what she asked, moving the bottle carefully in front of the glass. As the light hit the angles of the crumpled plastic bottle and then passed through the water, it spread out the other side in a subtle cascade of color. Like a rainbow.

“The angles of the bottle and the refractory properties of the water act as a makeshift prism, which separates the wavelengths of light,” she began, but Nick’s expression made her stop.

He was staring through the bars and into the elevator shaft, his eyes aimed up at the gilded urn. Where the colors of the prism hit it, the surface of the urn suddenly looked different. Clearly visible in the metal right beneath the rim were two rows of numbers.

“Christ,” Adrian whispered, behind them.

“No, Newton,” Hailey said. Even so, she could hardly believe she had been right. “That urn is gilded—maybe bronze, which is mostly copper—or maybe gold. When you shine regular sunlight on it, it appears to reflect the light back evenly—but it doesn’t. Both gold and copper reflect the red wavelengths in light well, but blue and green wavelengths poorly. But if you lace in another metal with different reflective properties—say, wisps of silver, or rhodium—when you use a prism to break the light up into its constituent parts, you get a much higher contrast in the green, blue, and violet spectrum. As you can see.”

“So those numbers were always there,” Nick said. “Written in tiny amounts of silver or rhodium—but you can’t see them unless you use a prism.”

Nick was staring at the urn like he was witnessing magic. But it wasn’t magic at all, it was science. And the numbers on the urn—

“It’s the key, right?” Nick said. “To decipher the letters in the book.”

“Jefferson’s perfect cipher,” Hailey said.

“Thomas Jefferson’s cipher?” Adrian gasped.

Hailey nodded.