"Come here," he said. I followed him into the lab. He indicated a microscope. His eyes were bright.

"Well?"

"A drop of my blood," he said. "Look."

I squinted into the microscope. I saw purple discs. Oddly, they did not attack the red blood cells. There was no fission, no mitosis. The leucocytes, strangely enough, let them alone.

My hands were shaking as I took a sterile slide and pricked my finger. I put the slide under the microscope. I adjusted the lens and stared.

Purple discs, swimming in my bloodstream. Thriving. Minding their own business.

"Me, too," I said.

"They're inert," Max said hoarsely. "They don't affect metabolism, cause fever, or interfere with the body chemistry in any way. Do they remind you of anything?"

I thought about it. Then I went to the slide file that was marked flora—negative.

"Right," Max said. "The purple thistle. Spores! The atmosphere is clogged with them. Greta, my sweet, we're infected."