“Go on, you first,” Mercy told Inspector Galeano, who nodded at her and made the leap to the engine.

“I’m right behind you!” she said. And there, at the edge of the engine, Mercy Lynch eyed the ledge between herself and the machine. She crossed it with two short steps—grabbing the handrails on either side of four stubby stairs that led into the engine’s pilot chamber—as she watched the retreating feet of the Mexican inspector climbing above her and disappearing over the side.

Behind her, something screamed.

It didn’t sound like a woman, or a man either. The scream was parched and broken, and it was god-​awful close.

Mercy turned around and saw—right behind her, nearly on her heels, in the spot between the ammunition cart and the back edge of the Dreadnought—a man who was not a man any longer.

She saw his face and it reminded her of other faces. The wheezers in the Robertson Hospital. The dying men in Memphis, lying strapped to cots and begging for the very thing that was killing them. The bodies in the sealed-​up caskets that had been in the rearmost compartment of the train only hours before.

This face was the same.

It was grayish, with yellow pus and sores around the edges of every membrane. Its eyes were sunken and dry, withering in its skull like raisins. It sat atop a body with flesh that was beginning to slough off, wearing clothes that were only mostly intact, missing buttons, patches, pockets, and other pieces that could be snagged and removed.

But this face.

This face was snarling, and approaching her.

The corpse-​man reached for the handrails, just as Mercy had done. While it grabbed, its mouth tried to grab, too—it gnawed at the air in the space between them and snapped at her shoes.

And although she’d spent her adulthood saving lives . . . and although she’d never, not even accidentally, killed a man . . . she seized one of her guns and she fired at the wrinkled space between the corpse-​man’s eyes.

He was so close that when his skull exploded, bits of his brain and face splattered across everything, including Mercy’s cloak and dress. Pieces of him slid down slowly off the hem of her skirt, dripping and plopping down between the tracks.

The rolling noise of grunts and screams and groans was all around her now, closing in and pinning her down like a tangible pressure. But she shook it off, and she turned and she climbed—up into the engine, where the inspector was holding his hand down to her, calling, “Here! Climb up!”

She scrambled and seized his hand, and let him help her up over the side, where Lieutenant Hobbes and the conductor were frantically throwing levers, pressing buttons, and shouting directions to the men who were trying to affix the snowplow to the front of the train.

But the swarm was upon them, as if that first corpse Mercy had shot down was only the scout, and the rest were right on its heels. She climbed up on a bin and saw the men out front trying to move the snowplow into place draw their guns and begin shooting, trying to clear a big enough patch that they could work those last latches, bolts, and pulleys and get the train moving.

Behind her, the boiler was coughing and straining its way to full power once more. The stretch of the superhot metal made ghastly whimpers, as if it, too, understood the necessity of leaving, and leaving now.

Lieutenant Hobbes leaped to the foremost edge of the western wall, leaning forward and aiming outward. He fired, providing cover for the men below.

Mercy positioned herself on the east side, and Galeano climbed up to stand with his feet planted apart atop the conductor’s shed. He flexed his wrists, checked his bullets, picked his targets below, and with an anguished shout, opened fire on his undead countrymen.

The nurse followed suit.

She fired off one shot, then two. Aiming down, hitting them in the heads and necks. Exploding their skulls away from their bodies, leaving their arms and legs to splay and sprawl and collapse to the ground. She refused to look past the circle where five men were ratcheting the snowplow into place. Right there, in that circle, the undead were sweeping down on the workers in ones and twos. But beyond that circle, appallingly close, they were coming in fives and tens. In dozens. In hundreds.

But she had only two hands, and only so much ammunition. The satchel she wore was slung across her back, freeing up her arms and elbows so she could aim and shoot, sometimes hitting and sometimes missing. One head. Two heads. A puff of snow like dust, right in the place where a corpse had only just been running. She missed another one, and couldn’t recall how many shots she’d fired.

Below her, the five men were dividing their time between self-​defense and the task at hand, and the task at hand was losing ground. Above her, Inspector Galeano was still shouting, still shooting; and beside her, Lieutenant Hobbes was reloading.

Mercy’s right gun ran out of bullets. She whipped her satchel front and center, dug around hastily, and filled both wheels of both guns with quivering fingers gone numb from cold and recoil and fear.

Lieutenant Hobbes said, “Mrs. Lynch!”

And she said back, “I’m reloading!”

“Hurry!” And he fired again, and again.

She clapped the wheel of her left handgun into place, fully stocked once more. Mercy dared a glance up ahead at the Shenandoah. Her heart constricted as she saw the Confederate men holding their position with prybars and long-​barreled guns that were long empty. They used them like bats, swinging and swatting the attackers away as long as their arms could stand it.

“Mrs. Lynch!” It was the conductor this time. She’d never caught his name, and didn’t know where he’d picked up hers, except from standing around and listening to people shout it.

She responded by aiming and firing again, as the wave kept coming and the men below kept working.

A dead woman was running in fast, her full skirts in bright colors and patterns layered up together. Her arms were bare, despite the frigid temperatures, and her hair was as wild as a squirrel’s nest. This dead woman’s face was contorted, her lips drawn back and her jaw thrust forward; she was reaching with her teeth.

Mercy aimed carefully. She waited until the woman’s eyes looked wet and near, and her scream could be discerned as an individual cry above the echoing cacophony of the bizarre battle.

And she fired. She pulled the trigger once, and watched the top of the dead woman’s head shatter. Her legs kept moving, only for a few steps more; then she stumbled to her knees, and then forward into the snow. But at least the corpse hadn’t reached the porter, who was beginning to climb up the side of the snowplow; and it hadn’t reached the rail-​yard man, who was hot on the porter’s trail.

The rest of them, though. They were still coming.

Inspector Galeano screamed, “Ay, Dios mío! Keep it clear!” He fired the last three bullets in his barrel and seized at his own ammunition bags, hunting for more. “They are coming! They are still coming!”

The conductor hollered something down at the men on the snowplow, but Mercy didn’t catch it. She was focused on following directions, on keeping the spot in front of the train clear of the climbing, clamoring bodies with their clamping teeth and corpses’ eyes.

Right under her arms, the first porter rose up so that she was shooting past him, over his head. She was surely giving his ears a terrible thrashing, but he didn’t complain. He said at the top of his lungs, “Clear! Fire and start!”

This startled Mercy into looking over at the lieutenant. She saw two of the other rail men coming up over the edge beside him; and then she understood that the men on the ground in front of the train were finished, and the snowplow was readied, and they could leave, if only they could barrel through the barriers before them. She holstered her guns and they sizzled hot against the leather, smoldering warm patches against her hip.

“Here,” she said to the porter, who struggled to lift himself over the edge. She took him by the shoulder, under the arm. “Here, come on. Get up here.”

He fell down past her, into the Dreadnought’s interior, and she reached for the rail man.

The rail man gazed up at her in terror. He kicked hard, knocking away a corpse’s teeth as they nipped and chomped at his boots. He was struggling, his striped shirt ripped and the jacket he wore over it hanging from one arm.

Mercy braced her feet around a pipe that was down by her knees, reached over the edge, and seized his forearms even as he grasped at her wrists. He was heavy, but she was strong. She’d lifted a pony once or twice, and plenty of men at the Robertson Hospital, when it’d come to that. She could lift him, too.

She heaved him backwards, and up, and with an awkward sideways slide over the rim, he toppled down into the interior, gasping for breath like a freshly caught fish in the bottom of a boat.

The conductor was moving, a man with a mission and maybe—God willing—a plan. “Help me!” he said to the lieutenant, who was still firing potshots as the uniformed dead began to climb, using their fallen brethren as ladders and stepstools on their way ever higher, trying desperately to make it up to the living folks inside the iron giant.

Lieutenant Hobbes holstered everything, leaped off the bin, and joined the conductor beside a pair of metal levers that were as long as a tall man’s thigh.

“On the count of three—pull that one!” the conductor said as he pointed.

“Count of three,” the lieutenant repeated.

“One, two, three—” And the levers both came down, not easily, but with the strain of both men’s backs cranking and pulling with all their weight.

A snapping latch cracked almost as loud as the guns, and the balance of the engine shifted; Mercy felt it as a slight leaning forward, where before the engine had seemed to point up just a touch.

“It’s on!” said the rail man. His observation was picked up and echoed around the narrow space. “It’s on! It’s on!”

The conductor’s mouth was a line as hard as a riveted seam. He said, “Let’s go.” He drew down on the whistle, and the edge of his gray mustache twitched with determination, or rage, or desperation, or something else Mercy couldn’t quite read.