“Tell us how to find these caches of supplies,” Tanq says, and she’s leaning forward, eyes bright. I’m not sure what it is about supplies that has her so excited.

“They’re marked,” Manny says. “We used a symbol common enough throughout the world that they wouldn’t attract Farmer suspicion.”

“The Null sign!” Tanq blurts.

“Yep. Only the red ones mark caches. All the others are just there for camouflage. The Farmers are colorblind.”

“Interesting,” Trey says. “And they don’t see into shadows very well. . . . Their vision must have evolved completely differently than ours did. The one we saw didn’t have eyes—more like depressions in its face, like it had eyes once upon a time, but they were a vestigial organ that gradually disappeared. . . .”

“Wow,” says Wyatt. “You don’t talk like a Black guy at all.”

Trey’s face freezes. He takes a deep breath through his nose.

“Holy shit,” Tanq says.

“Huh?” says Wyatt.

“Congratulations on being racist even in the apocalypse,” Tanq says.

“What? I was just observing . . . There’s nothing wrong with—”

“Wyatt,” I say. “Now is not a good time for you to talk.” It’s something Shawntelle used to tell me whenever I said something ignorant.

“One of the reasons Trey was chosen,” Manny says carefully, not seeming to address any one of us in particular, “was his natural curiosity and his aptitude for STEM fields.” He pins Trey with a gaze. “So, you saw one? A walker?”

Trey squares his shoulders, as though throwing off what just happened. I wonder how many times throughout his life he’s had to brush away moments like this. “Yeah, at the Ohio State Medical Center. Strangest thing I’ve ever seen. But also strangely humanlike. Maybe humans and Farmers had a common ancestor?”

Manny nods. “Some of our friends at SETI speculated about that exactly,” he says. “I mean, the panspermia hypothesis has been around a long time, and—”

“Back to the Null sign,” Tanq says. “We look for the red ones?”

“Exactly. We spent the last couple of years blanketing the whole world in null signs. Well, and theta signs, but that was mostly in Russia. The Farmers will see those symbols everywhere. But only survivors will be able to tell which ones mark caches or lead to facilities.”

Tanq starts giggling, and I think I know why.

“That graffiti artist in Columbus,” I say. “Called himself Null. He tagged the whole city with that symbol.”

“Columbus cops hated him,” Trey says. “Several guys on my team had to do community service one summer. Spent the whole time painting over null signs. Seemed pretty useless. They’d just reappear.”

“Null was not just one person,” Manny says. “There were many, many Nulls, all over the world. It became a cultural touchstone in Ohio. In Madrid too, though there they call him El Nihilista.”

“Wyatt, did you ever see a null symbol in Ann Arbor?” Trey asks. A peace offering.