“That sounds like Sherman,” said Dr. Cale. There was a bleak note in her voice, like she was making light commentary to keep herself from starting to scream. “He used to say that gender was a construct of the body and the mind, and that since his mind was a hermaphroditic worm dreaming of being a gendered biped, he felt no reason to restrict himself any further.”

“But when did he leave here?” I pressed. I vaguely remembered Tansy saying something about him disappearing from the lab six months before I had—before Sally had—before the accident, but I wanted to be sure. So much had happened during my brief visit to SymboGen that I no longer completely trusted my recollections. “Tansy said something about my accident…”

“Yes,” said Dr. Cale wearily. “He left here about six months before Sally Mitchell lost control of her car. I had just finished doing my monthly check on the chimera—”

“The what?” interrupted Nathan.

“Adam, Tansy, and Sherman: my chimera,” said Dr. Cale. “People—and they are people, anything that can think and communicate and tell you what it prefers to be called is a person, regardless of species or origin—who were created by combining multiple organisms. It’s a medical term, usually, for beings that have multiple distinct types of DNA in their bodies. It’s frequently used for people who absorbed their twins while they were in the womb, to give a common example. In mythology, a chimera is a creature made up from bits and pieces of different animals. I use it for the hybrids. It sounds less… judgmental than ‘parasite’ or even ‘symbiont.’ ”

“So that means me too, now,” I said quietly. Dr. Cale glanced at me, looking almost guilty. I shrugged. “It’s okay. I like it. And you’re right—it’s a better word than ‘hybrid,’ or ‘freak,’ and those were really the only things that I was coming up with. What kind of check were you doing?”

“Making sure there was no tissue rejection or complication, that their human immune systems hadn’t suddenly started attacking their tapeworm bodies as invaders, that there was no mismatch between the neural network and the activity coming from the worm—all fairly standard.” Dr. Cale must have read the dawning disgust in my expression, because she hastened to add, “Dr. Banks was performing very similar tests on you. Chave confirmed it for me, starting when you were brought back to SymboGen for neural mapping. I would have intervened much sooner if I thought that you were in any danger of rejection.”

I wanted to believe her, I really did—I was her tapeworm “daughter,” after all, and I’d been dating her biological son for several years. She had every reason to want to help me stay healthy and psychologically intact. But she wouldn’t meet my eyes, and I had to ask myself whether she’d been viewing me as a true control group: something not to be touched or interfered with, because that would have spoiled her data.

“So Sherman left right after you gave him a clean bill of health,” I said slowly, trying to select the words to make what I was saying both inoffensive and clear. “Did you say anything like ‘this means you’re stable’ or ‘this proves the interface can sustain itself in the long term’ or ‘yay, you’re not going to melt’?”

Dr. Cale frowned. “Maybe…”

Sometimes smart people can be a special kind of stupid. The kind where they know so many facts and are so good at saying “no one would ever do that” that they somehow manage to convince themselves the world is going to care about what they think. It’s like they believe that intelligence alone defines the universe. “So what if he saw that as permission?” I asked. “He left, and he knew what he was, and that humans had created him, and that maybe there was a way to make more like him. And then I happened, and he realized that it could happen naturally. You knew what the signs looked like. So did Dr. Banks. Why wouldn’t Sherman?”

“You think he went to SymboGen specifically to begin engineering the downfall of the human race.” It wasn’t a question, and Dr. Cale didn’t sound horrified when she said it. If anything, she sounded… impressed. Like this was something any parent would absolutely want their son and protégé to think of doing.

I looked to Nathan, too baffled by her tone to know what to say. Thankfully, he wasn’t siding with her on this one. Expression hardening, he looked at her and asked, “Mom, do you think that what Sal is suggesting is possible?”

“Possible, yes,” said Dr. Cale. “Probable, given the rest of what we know… oh, yes. Sherman never went to college, for obvious reasons, but all of my chimera children have helped me in the lab as part of their chores. He understands genetics at least as well as your average lab assistant, and probably better than the majority of them. He knew that we were going to have issues when the human population figured out that their implants had the potential to become sapient; he knew there was a chance that the chimera and human races would wind up competing for ownership of the planet. He could very easily have decided this was the appropriate way to approach the problem, and simply put his plans into action once he managed to find a sympathetic ear.”

“I don’t understand how anyone could think handing their bodies—and their world—over to a different species was a good idea,” I said.

“Humans have done a lot to damage this world, Sal,” said Dr. Cale. “The idea of keeping our human bodies, which are useful things for manipulating the environment, but replacing their brains with something that might be a little kinder…”