more startled than frightened but lost her balance for a moment and threw her right foot out to the side to steady herself. Her boot squished through something soft before finding solid ground next to the tank, but it was too little too late; she was past the tipping point and on her way down, right into whatever she’d just stepped in. She watched as the ground moved up toward her in slow motion.
And then she was moving upward again. With one strong, controlled tug on the loop at the back of her suit, Roberto pulled her onto her feet next to him.
She looked up at him, grateful.
He smiled. “Careful.”
A voice called from nearby. “Hey.”
They turned. Trini was standing on the roof of the house, about ten feet above them. “I found Uncle.”
It wasn’t much of a climb, even in the suits. First onto the hood of the car, then one big step up onto the porch roof, then a sort of jump with a shoulder roll, and they were all the way up. Roberto went last, so he could give Hero a shove up onto the roof if needed, and he was so preoccupied with making sure she didn’t fall that he failed to notice the sole of her boot, even when it passed within a foot of his face. He would have had to be pretty eagle-eyed to see it anyway, because there wasn’t much of the stuff, but it was there.
Near the heel, between the fourth and fifth hard rubber corrugated ridges of her right boot, there was a smear of green fungus she’d picked up when she lost her balance back at the tank.
Hero scrambled the rest of the way over the edge of the roof, Roberto flipped himself up to join her, and they walked the few paces over to where Trini stood looking down at something. The wind and dust had picked up substantially, so her view was partially obscured, but Trini knew a human corpse when she saw one. This one was in rough shape. Uncle couldn’t have been dead for all that long, but the damage to his corpse was extensive, and it wasn’t postmortem. The flesh wasn’t mangled from the outside, by scavengers or weather.
“He exploded,” Hero said.
Boy, did he ever. What used to be Uncle was now a husk that had been turned inside out, everything internal made external. His rib cage was wrenched open cleanly and violently at his sternum, parted like a suit coat lying on the floor with nobody in it. His arms and legs were denuded of flesh, their bones pockmarked with what looked like more tiny explosions from within, and the plates of his skull had been split apart along their eight seams, as if the glue that held him together suddenly failed all at once.
Roberto, who had seen a lot of ugly things, had never seen anything like this. He turned away, and as he did so the wind let up, the dust cleared for a moment, and all at once he had an unimpeded view looking back the way they’d come. Every building in town was more or less the same height, and from up here on top of Uncle’s house, he could see onto all the other rooftops.
“Oh my God.”
The others turned and saw what he saw.
The rooftops were covered with dead bodies, every single one of them burst open in the same way as Uncle’s.
Roberto didn’t need to count to know there would be twenty-six.
AT THE MOMENT THEY STOOD ON THE ROOF, PIECING TOGETHER WHAT had happened to the residents of the doomed village, the fungus was busily at work between the corrugated rubber ridges of Dr. Hero Martins’s right boot. Cordyceps novus had reached a barrier, the hard rubber sole between the boot and her foot, and if there was one thing it hated, it was a barrier. But every good villain has a henchman.
In its mutated state, the fungus housed an endosymbiont, an organism that lived within its body in a mutualistic relationship. What the fungus couldn’t do, the endosymbiont could—in this case, catalyze the synthesis of random chemicals in a special new structure in order to break through barriers. It was like having your own chemistry set.
The endosymbiont, which lived on the surface of the fungus in the form of a light sheen, was exposed to the atmosphere every time Hero took a step. It absorbed as much oxygen as it could, combined it with carbon drawn from the dust and dirt particles that had stuck to the goo, and formed a tight network of carbon-oxygen double bonds. These carbonyl groups, now active ketones, pushed their way upward, toward the sole itself, until stopped there by the hard, unyielding mass.
So it hybridized again. The new ketone sampled available elements from the rubber and dirt and dust and cycled quickly through a variety of carbon skeletons. It mutated into oxaloacetate, which is great if you want to metabolize sugar but no use getting through the sole of a boot. Undaunted, it mutated again, into cyclohexanone, which would have been good for making nylons, and then into tetracycline, superb if you’re fighting pneumonia, and then, finally and most damagingly, it recomposed itself as H2FSbF6—fluoroantimonic acid.
The powerful industrial corrosive began eating its way through the rubber bottom of Hero’s boot.
The mutation process so far had taken just under ninety seconds.
Hero, of course, was unaware of what was happening. As they climbed down from the roof and hurried back to the tank, she was distracted, trying to explain what they had just seen. The fungus, she speculated, was mimicking the reproductive pattern of Ophiocordyceps, a genus that consisted of about 140 different species, each one of which reproduced by colonizing a different insect.
“How’s it do that?” Trini had her gun out again and her head was on a swivel as they climbed down onto the roof of the car.
Hero explained: “Let’s say its target species is an ant. The ant walks along the forest floor, and it passes over a tiny spore of the fungus. The spore adheres to the ant, digs through its outer shell, and nests inside it. It moves through the body as quickly as it can, making its way to the ant’s brain, where the rich nutrients send it into an exponential growth phase, helping it reproduce up to ten times as fast as it would in any other part of the body. It spreads into every portion of the brain until it controls movement, reflex, impulse, and, to the extent that an ant can think, thoughts. Even though the ant is still technically alive, it’s been hijacked by the invader to serve its needs.” She jumped to the ground. “And the only thing a fungus needs is to make more fungus.”
Roberto looked around, understanding the town better now. Or the people, anyway. Jesus, the people, all of them.
Hero walked quickly to the tank and knelt down beside it, flipping open her sample case again. “The ant stops acting for itself. All it knows is it has to move. Up. It climbs the nearest stalk of grass, clamps its jaws down as hard as it can, and waits.”
“For what?” Trini asked.
“Until the fungus overfills the body cavity and it explodes.”
Roberto looked up at the roofs of the houses and shivered. “That’s why they climbed. To spread the fungus as far as they could.”
Hero nodded. “It’s a treeless wasteland. The roof was the highest spot they could find. You work with what you’ve got.” Her gloved hands picked carefully through the sharp metal tools in the case. She picked a flat-bladed instrument with a ring grip, slipped it over her right index finger, and flipped open a sample tube with her left hand. Carefully, she scraped as much of the fungus into the tube as she could. “It’s an extremely active parasitic growth, but that’s about all we’ll know until I can isolate the proteins with liquid chromatography and sequence its DNA.”
Roberto stared as she flipped the tube shut with a practiced gesture.
“You’re bringing it back?”
She looked up at him, not understanding. “What else am I supposed to do?”
“Leave it. We’ve got to burn this place.”
“Go right ahead,” she said. “But we need to take a sample with us.”
Trini looked at Roberto. “She’s right. You know she’s right. What’s the matter with you?”
Roberto