The Last Equation of Isaac Severy(40)

This map, however, she was starting to like. Her grandfather had been consumed with eliminating the city’s gridlock, but these dots showed no apparent relation to streets or freeways. Isaac had created a map that was about something else. But what?

“What about one of these numbers on the map?” she asked Alex.

He shook his head. “Wouldn’t make sense.”

“Why not?”

“It’s not impossible, but it would be . . . inelegant. These things usually have a certain something, an aha!?”

Hazel thought about their room number. “What about 137? Is that aha! enough?”

Alex smiled. “It’s the first number I tried.”

“Strange thing to call an eighth-floor room, isn’t it?”

“You know Isaac was fascinated with that number, don’t you?”

She didn’t answer right away. Instead, she found a piece of hotel stationery and jotted down for him the numbers Isaac had left inside the book cover—137.13.9. “Not until I saw this.”

He stared at the numbers for a long moment. “Where did you find these?”

“It doesn’t matter,” she said. “What do they mean?” When Alex started to enter it as a password, she stopped him. “I tried that.”

He tried various combinations of the numbers anyway and then sighed. “One thirty-seven is a spooky integer that shows up all over the place in math and physics. Most famously, it appears in a constant governing the interaction between charged particles, like electrons.”

Feeling her vision blur slightly with fatigue, Hazel took a position on the couch closest to Alex as he went on to explain how the Austrian physicist Wolfgang Pauli had been so obsessed with the number 137, it nearly drove him mad. As an old man, when his nurses were wheeling him into a room at the Rotkreuzspital in Zurich, the physicist looked up at the number on the door: 137. He reportedly groaned, “I’m never making it out of here.”

“And did he?”

“Pauli died in that room. Pancreatic cancer.”

Hazel frowned. “You don’t think Isaac meant to die in here, do you?”

He shook his head. “He’s got more subtlety than that. I think it was his idea of a joke. But these numbers, I have no idea.”

Maybe it was the way Alex spoke or maybe it was her increasing exhaustion, but any suspicions she may have had about him seemed to fall away.

“Why did Isaac never talk about you?” she asked.

He looked up, startled by the question.

“If Gregory or I ever asked about our cousin Alexis,” she continued, “Isaac and Lily were always cagey.”

He gave her a mischievous smile. “Are you doubting my identity, Hazel?”

“Well,” she said, a smile breaking on her own face, “I am taking your word for it that you are who you say you are. You could have the real Alexis bound and gagged somewhere, for all I know.”

Silently he reached inside his jacket, produced an EU passport, and handed it to her. Hazel flipped past a collage of stamps to his bearded image, casually confronting the camera. She read the name: Severy, Alexis James.

“You didn’t take your father’s name?”

“I changed it, first year at university.” He took back the passport. “Though it wasn’t to flatter my mother, believe me. I suspect the reason Isaac never talked about me is because he was deferring to his daughter, who preferred to leave my existence vague.”

“That doesn’t surprise me,” Hazel said. “I’ve never been a big Paige Severy fan. Sorry.”

“Don’t be. My French financier father is even less enthusiastic about parenting, if you can imagine. Sent me off to boarding schools all over Europe, making sure to ship me far from where he was living at the time. I had to seek out what information I could about both sides of the family—the Severys being the far more interesting of the two. But my mother made it very clear that she found having a child inconvenient, and I think she did her best to bury my existence. She gave birth to me in relative secret and didn’t bother telling anyone until years later, even when I started to show real academic promise. Even then, she didn’t bother to correct anyone’s confusion over my androgynous name.”

He laughed softly. “It’s funny, but I knew Isaac mostly as a fan of his work, not as a relative. I can count my actual visits with him on two hands. When we finally met for the first time on one of his trips to England—I was in middle school—I felt as if I’d known him forever. It was this moment of ‘Oh, there he is. There’s my family—’?”

He stopped short, and Hazel thought she detected a glisten in his eyes, but Alex quickly blinked it away.

When he fell silent, she leaned in closer. “We may have had slightly different childhoods, but actually, I had a very similar experience with him.” She looked down, aware of how close their knees were to touching. “Isaac had a way of making you feel immediately . . . ”

He looked up. “Like a part of something great?”

“Yeah,” she said, with an intensity that surprised even her. “It was like he had chosen you to join some thrilling spy ring.”

He smiled. “I wouldn’t have put it like that, but yes—as if all that stood between the world and an Axis victory was you.”