“So you’re basically saying we’re all stupid,” Alex said.

Chatterjee shook his head. “I’m saying that part of being a kid, a teenager, is that you literally don’t have the capacity yet to think fully about the consequences of your actions.”

Alex cut in: “Where have I heard that before?”

Patrick had leaned back around the doorjamb to spy on the Hosts outside. Chatterjee yanked him back, as if proving his point, while barely slowing down. “That’s why teenagers can be impulsive, angry, lovesick, higher in risk taking—”

“Well,” Patrick said. “We’ll need risk taking now.”

“That’s absolutely true. But if what Chance is saying is correct, then this airborne parasite invades its host and gains control by spreading through the white matter, seizing control of the frontal cortex.” He waved the clawhammer in a circle. “From there it takes over the brain and the nervous system, manipulating the host like a puppet. It can run the human body as if it’s a machine, operating the muscles without regard for pain or injury.”

I thought about Uncle Jim’s death shudder. All those men we’d seen out there, walking their mindless spirals. Coach Hanson scrabbling forward to get us, not even caring about the bone sticking out of her leg.

I suddenly understood. “So if the parasite is spread through white matter, the frontal cortex—the puppet master—has to be covered with white matter for it to become infected. Or else the spores have no pathways to get to our brain’s control centers.”

“That’s right!” Dr. Chatterjee said. “Which means the thing that makes it harder for teenagers to formulate mature decisions is the same thing that saved you. And saved me.”

Suddenly I felt much younger than my fifteen years. There it was, tightening around my spinal cord, that same sensation I’d felt as a six-year-old waking up to Sheriff Blanton standing on our porch, shifting awkwardly from boot to boot, hat in his hands, bad news on his face. That feeling of bone-deep aloneness, as if I’d been set adrift, a boat left to navigate across the rocky slate of the ocean. If what Dr. Chatterjee was saying was true, then the people least equipped to make good decisions were the only ones around Creek’s Cause left to make them.

Like me.

But Patrick was still focused on Chatterjee. “Why’d it save you?”

“Do you know what causes multiple sclerosis?” Chatterjee asked.

We all shook our heads.

“White-matter lesions.” He smiled. “I have enough holes in my brain that the parasite couldn’t take me over either.” Turning, he started back up the hallway, wobbling past the cracked-porcelain bank of water fountains. I hurried to keep up, Cassius scampering along at my side. With his big strides, Patrick had no problem regaining the lead.

“Your weakness is your strength,” Patrick said.