The figures were coming so fast, and running so low, she could hardly believe her eyes.

And then she felt an even greater chill clutch at her heart, as she realized what the running shapes really were.

She whipped around toward the boat again, but it had already been dislodged and was disappearing into the fog.

Had she come so far … for this?

But she was too exhausted, too paralyzed with cold and despair, even to try to save herself.

She stared in terror down the beach as, shoulders heaving and eyes blazing orange in the dusk, the pack of ravening black wolves galloped toward her across the rocks and sand.

“You okay, Major?”

Slater knew what he looked like, and he knew why Sergeant Groves was asking. He had taken a fistful of pills that morning, but the fever was back. He put out a hand to steady himself, then yanked it back off the hood of the jeep. The metal was as hot as a stove.

“I’ll survive,” he said, rubbing the tips of his fingers against his camo pants. That morning, he had visited the Marine barracks and watched as two more men had been airlifted out, both of them at death’s door; he wasn’t sure they’d make it. Despite all the normal precautions, the malaria, which he’d contracted himself a year before on a mission to Darfur, had decimated this camp. As a U.S. Army doctor and field epidemiologist, Major Frank Slater had been dispatched to figure out what else could be done — and fast.

The rice paddies he was looking at now were a prime breeding ground for the deadly mosquitoes, and the base had been built not only too close by, but directly downwind. At night, when they liked to feed, swarms of insects lifted off the paddies and descended en masse on the barracks and the canteen and the guard towers. Once, in the Euphrates Valley, Slater had seen a cloud of bugs rising so thick and high in the sky that he’d mistaken it for an oncoming storm.

“So, which way do you want to go with this?” Sergeant Groves asked. An African-American as tough and uncompromising as the Cleveland streets that he hailed from—“by the time I left, all we were making there was icicles,” he’d once told Slater — he always spoke with purpose and brevity. “Spray the swamp or move the base?”

Slater was debating that very thing when he was distracted by a pair of travelers — a young girl, maybe nine or ten, and her father — slogging through the paddy with an overburdened mule. Nearly everyone in Afghanistan had been exposed to malaria — it was as common as the flu in the rest of the world — and over the generations they had either died or developed a rudimentary immunity. They often got sick, but they had learned to live with it.

The young Americans, on the other hand, fresh from farms in Wisconsin and mountain towns in Colorado, didn’t fare as well.

The girl was leading the mule, while her father steadied the huge baskets of grain thrown across its scrawny back.

“I’m on it,” Private Diaz said, stepping out from the driver’s seat of the jeep. His M4 was already cradled in his hands. One thing the soldiers learned fast in the Middle East was that even the most innocuous sight could be their last. Baskets could carry explosives. Mules could be time bombs. Even kids could be used as decoys, or sacrificed altogether by the jihadis. On a previous mission, Slater had had to sort through the rubble of a girls’ school in Kandahar province after a Taliban, working undercover as a school custodian, had driven a motorcycle festooned with explosives straight into the classroom.

“Allahu Akbar!” the janitor had shouted with jubilation, “God is great!” just before blowing them all to kingdom come.

For the past ten years, Slater had seen death, in one form or another, nearly every day, but he still wasn’t sure which was worse — the fact that it could still shock him or the fact that on most days it didn’t. Just how hard, he often wondered, could a man let his heart become? How hard did it need to be?

The girl was looking back at him now with big dark eyes under her headscarf as she led the mule out of the paddy and up onto the embankment. The father switched at its rump with a hollow reed. The private, his rifle slung forward, ordered them to stop where they were. His Arabic was pretty basic, but the hand gesture and the loaded gun were universally understood.

Slater and Groves — his right-hand man on every mission he had undertaken from Iraq to Somalia — watched as Private Diaz approached them.

“Open the baskets,” he said, making a motion with one hand to indicate what he wanted. The father issued an order to his daughter, who flipped the lid off one basket, then waited as the soldier peered inside.

“The other one, too,” Diaz said, stepping around the mule’s lowered head.

The girl did as he ordered, standing beside the basket as Diaz poked the muzzle of his gun into the grain.

And just as Slater was about to order him to let them move along — was this any way to win hearts and minds? — a bright ribbon of iridescent green shot up out of the basket, fast as a lightning bolt, and struck the girl on the face. She went down as if hit by a mallet, writhing on the ground, and the private jumped back in surprise.

“Jesus,” he was saying over and over as he pointed the rifle futilely at the thrashing body of the girl. “It’s a viper!”

But Slater already knew that, and even as her father was wailing in terror, he was racing to her side. The snake still had its fangs buried in her cheek, secreting its venom, its tail shaking ferociously. Slater pulled his field knife from its scabbard — a knife he normally used to cut tissue samples from diseased cadavers — and with the other hand grabbed for the viper’s tail. Twice he felt its rough mottled surface, strong as a steel pipe, slip through his fingers, but on the third try he held it taut and was able to slice through the vertebrae. Half of the snake came away with a spill of blood, but the head was still fixed in its mortal bite.

The girl’s eyes were shut and her limbs were flailing, and it was only after Groves used his own broad hands to hold her down that Slater was able to pinch the back of the dying viper’s head and pull the fangs loose. The snake’s tongue flicked like a whip, but the light in its yellow eyes was fading. Slater pinched harder until the tongue slowed and the eyes lost their luster altogether. He tossed the carcass down the embankment, and Diaz, for good measure, unleashed a burst of shots from his rifle that rolled the coils down into the murky water.

“Get me my kit!” Slater hollered, and Diaz ran to the jeep.

Groves — as burly as a fullback but tender as a nurse — was crouched over the girl, examining the wound. There were two long gashes in her cheek, bloody smears on her tawny skin. The venom, some of the most powerful in the animal kingdom, was already coursing through her veins.

Her father, wailing and praying aloud, rocked on his sandaled feet. Even the mule brayed in dumb alarm.

Diaz handed Slater the kit, already open, and Slater, his hands moving on automatic pilot, went about administering the anticoagulant and doing his best to stabilize her, but he knew that only the antivenin, in short supply these days, could save the girl’s life.

And even then, only if it was used in the next hour.

“Round up the nearest chopper,” he said to Diaz. “We need to get this girl to the med center.”

But the soldier hesitated. “No offense, sir, but orders are that the med runs are only for military casualties. They won’t come for a civilian.”

Groves looked over at Slater with mournful eyes and said, “He’s right. Ever since that chopper was shot down three days ago, the orders have been ironclad. EMS duties are out.”