So much of the way she had always interacted with me made sense now. So much of it still needed to be made sense of. “No,” I said. “It changes everything.” The broken doors that Dr. Cale had spoken of so often were open now; I could no longer pretend that they were just a children’s story, something I could safely forget about or ignore.

I looked back to Nathan, raising my eyes to his face and searching for any sign of rejection or revulsion. I didn’t want to leave him, but I didn’t want to make him stay with me if he couldn’t deal with the reality of what I was. I wasn’t sure I could deal with the reality of what I was—the calm I was feeling was probably shock, and would pass, replaced by hysteria. Better to make my choices now, when I could trust myself, than to let it wait until I was no longer thinking clearly.

How was I thinking at all? A tapeworm, no matter how cunningly engineered, didn’t have the size or complexity to think human-sized thoughts—but I managed it somehow. I had to be… the tapeworm part of me had to be driving Sally Mitchell’s brain, using it as storage somehow, like a person uses a computer. The thought made my stomach clench, and so I focused back on Nathan, who was safe; Nathan, who had never known Sally, but had fallen in love with Sal, with me, with the girl who had helped her injured sister into his office. He’d never batted an eye at any of my idiosyncrasies. Sally’s family had learned to love me when I replaced their daughter. Nathan had never needed to forget a person I could never be. That had always been so valuable to me. I was starting to understand a little bit more about why.

He met my eyes unflinchingly, and all I saw there was concern, and hope, and yes, love. He looked the same as he always had: black hair, brown eyes behind wire-framed glasses, golden-tan skin, and a serious expression that could spring into a smile at any moment. I didn’t see any fear or dismissal, or even dismay, in that face. I blinked.

“You knew,” I said, bewildered. “How did you know?”

“I told him.” Dr. Cale sounded tired. I pulled away from Nathan and turned to face his mother, who was pale where he was dark, from her sun-deprived skin to the watery blue of her eyes and the ashy blonde of her hair. Her shoulders sagged as she looked at me, and she said, “Back in my lab, when you were asleep on Adam’s cot. I thought he should… I’m sorry, Sal, but I thought my son should know that his girlfriend wasn’t entirely human. You clearly weren’t ready to have the same conversation. Perhaps it was wrong of me.”

“I think maybe it wasn’t,” I said slowly. “I wasn’t ready to know this yet. I wasn’t letting myself know this yet.” I looked down at my hands. “But I was going to figure it out.” I had already figured it out, and then locked the knowledge away from myself, as if that sort of thing had ever done any good. Once the signs had been placed in front of me, they had been too easy to follow. I would have followed them again, and maybe then, I wouldn’t have been able to make myself forget. “I needed Nathan to know before I did. I needed him to have time to come to terms with it. Because if he’d left me then…”

If Nathan had been having his own freak-out at the same time I was having mine, I don’t know how I would have gotten through finding out the truth about myself. Having him pull away from me then—even temporarily—would have devastated me. Here and now, in this lab, with Tansy missing and Sherman alive but suddenly my enemy, losing my humanity was a huge step toward the abyss. Nathan had been able to place himself between me and that long, final fall, and he’d only been able to do it because he’d already known what I was.

Dr. Cale nodded. “I’m glad you see it that way. That’s what I was hoping for.” She paused, watching me carefully before she continued: “I know you’re in shock right now, and I know we’ve all had a difficult day, but do you think I could have that thumb drive?” She grimaced. “I hate to ask you. I hate to even be here right now. You deserve this moment. But I need that data.”

My eyes widened. “I forgot.” I had been refusing to give her the thumb drive full of information stolen from the SymboGen computers until she gave me the answers I thought I wanted. But then I’d been distracted by the need for blood tests and MRIs and then… “I’m sorry.”

“It’s all right.” Now the glimmer of a smile touched her lips. “You had other things on your mind.”

The words sounded faintly unreal, like she was quoting them from a book or movie, something that showed how an ethical mad scientist would behave. I pulled away from Nathan entirely, bending to rummage through my discarded clothing until I found the thumb drive in the front pocket of my jeans. I walked over and held it out to Dr. Cale, who took it without commenting on the fact that I was still wearing nothing but an unbuttoned lab coat. Between Tansy, Adam, and… and Sherman, she must have gotten used to people whose sense of modesty was somewhat less developed than the norm.

“Thank you, Sal,” said Dr. Cale, taking the little plastic rectangle gently from my fingers. “You have no idea how much we need this data.”

“What is it, exactly?” I asked. “Tansy said it would explain how some of the sleepwalkers were integrating more quickly with their hosts…”

“It’s easy to forget sometimes that Steven Banks is a genius,” said Dr. Cale, still looking at the thumb drive. There was honest regret in her voice. “He blackmailed me into working for him, but the only reason he could was because I knew I wouldn’t be doing the heavy lifting alone—he’d be there to help, and to carry it on when I couldn’t go any further. It’s easy to sit here and say, ‘I did it, it was all my fault; I am Frankenstein and this is my monster,’ but D. symbogenesis is Steven’s baby as much as it is mine. Maybe more, by this point, at least where the commercial models are concerned.”