Nathan, on the other hand, did want to know. “What did you do, Mom?” he almost whispered.

“I went back into my lab and got one of the early versions of D. symbogenesis out of cold storage. And then I implanted it in myself, so that I could carry it out of the building without anyone the wiser. Most of the employees already had Intestinal Bodyguards by that point, so testing for parasites wouldn’t give me away, and I suppose Steven just assumed I knew better than to risk ingesting an early-generation worm. He didn’t count on the power of sentiment.” Dr. Cale smiled wistfully. “That was my Adam. He was my first, and greatest, creation. You know, Nathan, he had just as much of my genetic material in him as you did? He was virtually your brother.”

“I don’t know whether I should be flattered or feel sick,” said Nathan. He looked like he was leaning toward the second option. I stepped closer to him, trying to lend support through proximity. He smiled at me a little, looking strained, and didn’t say anything. There wasn’t really anything to say.

“Feel like your mother is a genius, and be glad I was willing to share my genes with you, not just with your brother,” said Dr. Cale. She sighed. “I didn’t have a choice, Nathan. Steven was going to destroy my work, and he was going to do it so that if things went wrong with the worms, he could claim there’d never been any indication of a potential risk to human health. He was going to pin it all on me, and by extension, he was going to pin it all on you. How long do you think our connection would have stayed secret after I became the person who recklessly endangered the lives of millions?”

“Still,” said Nathan. He was staring at the white mass on the X-ray like he could find the outline of the worm in the blur. “It was a big risk.”

“And I paid for it.” Dr. Cale spoke with absolute calm. “I ingested Adam and left the lab. I had to wait a month for him to grow long enough that we’d be able to extract segments without killing him. We needed to keep him alive, as proof that there had been earlier generations—that D. symbogenesis didn’t somehow spring fully developed from a test tube and a set of irresponsible testing procedures.”

“Didn’t you take your antiparasitics after that?” I asked.

Dr. Cale nodded. “I did, because I am not a complete idiot, current evidence aside. Unfortunately for me, we’d never tested Adam’s generation inside a human host, and we didn’t realize what the results would be.”

“There was too much human DNA in the early generations,” said Nathan. “The antiparasitics might have made the worm sick, but they couldn’t kill it without being increased to a level where they’d kill you, too.”

“That’s exactly right. Sadly for me, we didn’t realize that at the time. I took my pills like a good girl, and I passed enough dead tapeworm segments that I was sure we’d managed to clear Adam entirely out of my digestive system. We had our samples, and that meant that we could re-create the living worm at any time if we needed it to prove what SymboGen had been doing. You have to remember, I developed the Intestinal Bodyguard. It was more my baby than anyone else’s, no matter how much Steven may try to rewrite history. I didn’t approve of the way he was going about things, but I truly wanted to see D. symbogenesis thrive. If people could find a way to coexist peacefully with the worms, everyone would benefit.”

“SymboGen more than anyone else,” said Nathan. “What happened?”

“I’m getting there.” For the first time, Dr. Cale’s voice was sharp, holding the snap of authority she needed to organize her own underground lab and control this many people. “What happened, Nathan, is that we didn’t realize the antiparasitics hadn’t worked until I began losing feeling in my legs. It was intermittent at first, just pins and needles. Bit by bit, it turned into a numbness that didn’t go away. It could still have been sciatica, brought on by hard living and exacerbated by stress. I thought I was working too hard. I thought I was getting old. I didn’t think that the antiparasitics might have driven my stolen tapeworm out of my intestine and into my abdomen. He was very clever in what he did and didn’t chew through—instinct is a powerful thing, and he didn’t want to kill his host—but when he reached my spine, he didn’t have anywhere else to go. He was too large to migrate upward at that point, which is the only reason I’m alive today. So he compressed my spinal cord more and more tightly, until the day he permanently compromised the nerves. I collapsed in the middle of the lab.

“My assistants performed basic medical triage, including the X-ray films I’ve posted on the light box for you to study. It was immediately clear that we would need to operate. Adam and I had reached the point at which we could no longer share one body, and while I hated to do it, I couldn’t cede the ground to him. I had too much work to do. They removed eight and a half pounds of worm mass from my pelvis and abdomen. Unfortunately, the nerve damage was not so easily undone. Barring medical advances that I probably won’t live to see, I’m staying in this chair.” Dr. Cale shrugged. “I suppose I’m not the first person to see hubris as an object lesson, but I’ve worked very hard to make up for it since then.”

“Mom,” said Nathan, sadly. “Oh, Mom.”

“Don’t feel sorry for me, now. It was for science, and as long as something is for science, it’s worth doing. It’s just not necessarily worth repeating.” Dr. Cale’s smile was sudden, and very bright. “Now that we have all that out of the way, there’s someone that I very much want you to meet. You needed to understand what had happened right after I left SymboGen before this would make sense to you. All right?”