He searches for something in a cardboard box. A book, maybe. A fresh femur. “After I was discharged, I made good use of my time. Studies show twin rats can withstand exposure to nerve agents and doses of ricin longer than single births. Twin human fetuses recognize each other as nonparasitic organisms in the womb. This ability to differentiate between good and bad foreign agents must have further utility.” His voice grows quiet, thoughtful. “What is it that makes the two of you together stronger than the one of you alone? Is it your blood? Your muscle tissue? Your cellular composition? I’ve tested each of these in my other subjects, and none has shown the strength to withstand chemical agents—none as I believe identical twin blood will. If I can prove that—” He breaks off and turns from the shelf, a cable trailing from his fist, his voice rising again. “If other scientists had had the courage Molinare did, the willingness to push boundaries, then Baptiste might not have had to die.”

The fervor that lights his eyes sparks a flicker of recognition in me. We were in Angela’s apartment, my second day here. Seb was trying to convince me of some extrasensory ability twins possess.

“What you’re looking for isn’t plausible,” I say now. “Some extrasensory thing, if it exists, doesn’t translate to cellular—”

His backhand connects with my cheek, slamming my head to the other side. Ringing fills my ear canal, like a gong struck inside my skull, then deepens to buzzing. An image from the Champs-Élysées fills my thoughts: Seb crushing a fly against his bare skin. No flinch. No wince. No spark of empathy.

Seb’s mouth pulls into a frown. “Do not dismiss me, Shayna. I will find a cure, whatever it takes.”

Angela continues playing deaf and dumb as Seb raises a type of syringe pump with a heavy cylindrical base—a small motor with a long cord trailing to his feet.

“Are you ready?”

“For what?” My voice is wispy, beaten.

“For your first tattoo.” Seb tightens the ink cartridge on the tiny motor. “Did you know the local traffickers like to brand their product? Once I dispose of your bodies, the police will observe these tattoos—and the gunshots I’ll administer to your heads—and conclude you were victims of human trafficking gone awry.”