“But the wind carried it right to where we found Mrs. McCafferty.” I couldn’t bring myself to mention that it was headed for our house, too, and town beyond. “That seems like a pretty big coincidence.”

“So you’re saying people are breathing it in, getting infected by it?”

I shrugged.

“What does that?” Patrick asked. “You’re the one who pays attention in science.”

I racked my brain. “Viruses, bacteria—” I cut off abruptly, heat rushing to my face.

“What?”

“Spores,” I said.

“Spores?”

“Remember what you said about parasites and hosts?” I asked. “Well, there’s this movie that Dr. Chatterjee showed in biology. About this kind of fungus. It’s like a parasite.”

I remembered the class: Dr. Chatterjee, walking his wobbly walk up and down the aisles with his leg braces, lecturing us in his singsong accent. He’d been our family doctor for years, treating Patrick and me since we were in diapers. Eventually his multiple sclerosis made it too hard for him to hold a syringe steady, so he’d retired to teach high-school science. He had to have a helper—usually me—write for him on the dry-erase board and input grades into the computer, but he needed no assistance when it came to being a great teacher. He also worked as the town coroner. I guess his hand tremors were less of a concern when it came to dealing with dead people.

“Okay,” Patrick said. “And what does this fungus do?”

I glanced back, made sure we were out of earshot of the kids. “It attacks ants,” I said.

“Ants?”

“It infects their brains, makes them fall out of trees. Then the infected ant—”

“The host.”

“Yeah. The host climbs the stem of the tallest plant nearby and clamps down its mandibles on the top of it. Know what it’s called? The death grip. The fungus eats the ant and then releases spores that drift all over the place and infect more ants.”

There was a pause, and I suddenly felt self-conscious for remembering this stuff. I was mostly in advanced classes, one or two grades ahead. Patrick had once told me that I seemed more at home in books than outside of them. He hadn’t meant it as an insult—he’d intended it as a compliment after I’d brought home another solid report card—but it had burned like one. I guess I still felt a touch of embarrassment talking about school stuff with him. Patrick, who was most in his element atop a horse at full gallop.

I glanced over and saw that his face wasn’t judgmental but thoughtful.

“So it makes them march to their death,” he said. “Like Mr. McCafferty.”