“Please, Seb. You’re . . . you’re a good person. You don’t have to do this,” I cry as he crosses the fifteen feet to me in deliberate strides. He halts before me in a jerking motion, reminding me of that day on the Champs-Élysées when he caught me shopping for large-brimmed hats. Something in his face drops—lessens the unfeeling determination he’s been wearing since he took us.

He surprises me by laughing. A blunted, empty sound that stops short. “Look at us, Shayna. Would you have imagined this, your first day here?”

I think back to Seb’s morose expression, mirroring my own grief, in the lobby of Angela’s apartment building. His deep-blue irises were red from crying, I had believed. “No, I wouldn’t have. I thought you cared about us.”

Something of that day’s emotions returns to his face, pinching his eyebrows together. “The only thing I have cared for, for a long while, is finding a cure.”

“For cancer?”

“For chemical weapons,” Angela whispers, legs tucked underneath her, huddled against the wall.

Seb stares past me, over my head. “That is correct. My brother died from one. I watched him expire, unable to help. Only to watch.”

Mustard gas, Valentin had said was the cause of death for Baptiste Bronn. I suck in a breath, then release it in a measured exhale—counting the seconds—not wanting to disturb whatever Seb seems to be reliving. “That’s terrible.”

Seb lowers his gaze to me. “Yes. Baptiste was taken from me. And I have been unable to truly rest since then.”

“What do you mean?”

“When I came back to Paris, I saw him in crowds, or believed I did. At the grocery, the park, the catacombs. Realizing my eyes were betraying me was a devastation all over again. Men and women, everyone, fools and noncontributors to society, were a constant taunt that Baptiste was not alive. It was not fair. Why should they continue to live and not my brother? It was not right.” His hands clench into fists at his sides, and I fight the urge to lean away from his tools of pain.

“What did you do?”

“I returned to the only thing I knew. To science, to search for a cure. At first, I tested existing theories to combat different forms of chemical warfare and disguised these tests as part of my hospital research. Then I realized, quickly, the field had become stagnant. Devoid of progress. Other studies, however—studies less palatable to some—showed parallels between the responses of human twins and those of test animals. Yet how could I find the resources to continue those studies?”

Angela and I exchange a glance, but neither of us breaks the spell by interrupting.