In Denver, the Dreadnought had experienced the addition of a piece of equipment that looked like it’d been forged in hell.

This new addition was a snowplow fixture as large as a small cabin, designed to replace the pilot piece in case of a storm—or, worse yet, in case of an avalanche across the tracks. The snowplow was circular and made of reinforced steel and cast iron, of such a size that four or five people could’ve stood within its opening. But inside the circular frame it was fitted with hundreds of interlocking and overlaying blades, angled to move snow, rocks, or anything else that was unfortunate enough to land within its path. It looked less like something made to move snow than something designed to bore tunnels in rocks . . . or process entire herds of cows into ground beef.

Every once in a while, often in the very deepest part of the night when things were the quietest, Mercy could hear something whistle or whisper among the mountain peaks and across the wide, blue lakes that met between them. So far away, and she could hear it faintly but sharply. It made her think of the prick of a pin left inside a dress after alterations: sudden, bright, and small, but faintly alarming.

One time, upon seeing that her car-​mate was still awake, Theodora Clay blinked sleepily and asked out loud, “What on earth is that noise?”—but not so loudly that any of the few travelers around her, all the remaining civilians, would awaken.

Mercy murmured, “I couldn’t say.”

“It sounds like another train.”

“It might be, someplace far off. There are other tracks, here through the mountains. Other paths.”

Miss Clay yawned and said, “Yes, I suppose. They must all feed together for a while, until the pass at Provo.”

“What’s so special about the pass at Provo?” Mercy asked.

Miss Clay said, “Supposedly it’s the only spot where the mountains are passable for hundreds of miles in either direction. All the railroads have made bargains, deals, arrangements; however it works. Everything going west goes through that pass, except the rails that run from Chicago to the coast, and the ones that go through New Orleans, through Texas. I expect it will be impressive. All those tracks, side by side. Crowded into one stretch like that. I wonder how long it runs.”

And then they slept. In the morning, there was breakfast in the caboose with the inspectors, who never seemed to sleep, but always seemed very, very watchful. After the inspectors had retired with their coffee, Miss Clay put in an appearance. She seemed to have a special sense for when the foreign men would be absent, so she could “eat in peace,” as she put it.

Mercy privately thought that it was very like a Yankee, to go to war over the rights of people whom you’d rather die than join for tea. But in the name of peace, she kept this to herself.

Malverne Purdue also kept to himself, in that corner beside the caboose’s rear exit. He’d become a fixture there, a signpost of a man whose duty was only to declare, “No trespassing,” and threaten to enforce it with the Winchester across his knees. By and large, he was ignored, except when one of the porters would ask him about a meal, or Oscar Hayes would arrive to relieve him for a few hours of sleep.

Mercy could see him from the corner of her eye while she sipped her coffee, which she liked a bit better than the tea, all things being equal.

Theodora Clay could see Purdue, too, though she went to great and chilly pains to pretend otherwise. If ever she’d once looked at him with a kindly eye, the world wouldn’t have known it now. A reasonable observer might’ve assumed that there had been some kind of falling out between them, but Mercy figured that Miss Clay was only keeping her gaze clear lest her eyes reveal something of their adventure in the rearmost car.

Tea came and went, and with it the dull daily routine of life aboard the train rolled on, every bit as monotonous as the tracks beneath the wheels. Mercy missed the two easy virtue girls who’d taught her how to play gin rummy; but they were gone, and even if Miss Theodora Clay had owned a deck of playing cards, Mercy wasn’t entirely sure she would’ve liked to play.

Soldiers patrolled the three remaining passenger cars, from the gold-​filled car up behind the fuel cars to the caboose, where a scowl from Malverne Purdue ended the circuit before it could reach the refrigerated compartment. Down to a man, they were tense and unhappy, all of them listening, always listening, for the hoot of a train whistle coming up along the tracks to meet them—trying to beat them—to the pass, beyond which there was no reasonable way for one train to sabotage another. On the far side of the pass, the rails went their separate ways once more; so if they weren’t caught before sprinting that span (which Captain MacGruder had told her was nearly thirty miles long), the odds of them being affected by the engine of southern origin were virtually none. If the Shenandoah didn’t blow up the tracks by then, the Rebs would be out of luck.

Mercy didn’t think to wonder what had happened to the doctor until someone mentioned that he’d debarked in Denver, same as almost everyone else. This peeved Mercy greatly. No military regiment, legion, group, or gathering ever went anyplace near danger without a medical professional in their midst, or at least that’s how it ought to go. And the truth was, even if Mercy had been a proper doctor with a proper doctor’s training and experience, she had only her small satchel filled with basic equipment at her disposal. Anything much more serious than a broken bone or a bad cut could only be managed, not treated.

She felt alone, in the middle of everybody—even the other civilians who hunkered in the center passenger car and read books or played cards or sipped out of flasks to pass the time. She was the only medical professional of any sort on board, which meant that every stubbed toe, every rheumy eye, and every cough gravitated her way for analysis and treatment. It was the nature of the beast, she supposed, but even these small ailments did little to punctuate the wary boredom.

No one ever really nodded off anymore.

No one ever really paid full attention to the books, or the cards, or the vest-​hidden flasks; no one enjoyed the passing scenery as the black-​and-​white mountains scrolled past and the freezing waterfalls hung along the dynamited cliffs like icicles off a gutter. No one listened with both ears to any of the chatter, or the rolling, pattering passage of the train. Everyone kept one ear peeled for the sound of another whistle splitting the icy air.

And finally, on the fourth day, they heard it.

It squealed high and sharp.

The whistle blew again, and the echo bounded around between the boulders and the tiny glaciers that slipped with monumental slowness down the perilous slopes.

And everyone seized up tight, hearts clenching and unclenching. One by one, everyone rose and went to the south side of the train, from whence the noise had come. And soon, all the faces on board—except perhaps the determined and devilish Malverne Purdue, and maybe the conductor, up front and invisible—were pressed up against windows that could not have been colder if they’d been sheets of ice instead of glass. Everyone breathed freezing fog against the panes, wiping it away with gloved hands or jacketed elbows. Everyone strained to hear it again, hoping and praying the first shriek had been a mistake, or had only been a friendly train, passing on some other track on the approach to the pass at Provo.

Norene Butterfield groped at her niece’s arm and asked, “How far are we from the pass?”

And Miss Clay said, without taking her eyes off the smudged, chilled window, “Not far. We can’t be far.”

“And once we get to the pass, we’re safe, aren’t we?”

But Miss Clay did not answer that part. She didn’t exchange the knowing glance Mercy shot her either, even though both of them knew good and well that the pass was a death trap if both trains were penned within it simultaneously. Only on the far side would they find anything like safety.

Mercy climbed down from the seat upon which she’d been kneeling, and whirled into the aisle. Horatio Korman had been hanging about in the third passenger car, and the captain had been hanging about in the first one—or else, in the car with the gold, from which she’d been specifically forbidden from entering again unless directly ordered otherwise. With this in mind, she turned to the right and headed for the rearmost door, opening the latch and dousing the steam-​warmed car with a torrent of frigid wind. She shut the door as fast as possible, tugging her cloak up around her head and pulling it tight over her ears, trying to filter out the worst of the blizzard as she felt about for the rail and the platform space over the coupler. She moved to the next car easily, despite the temperature and the wind that felt strangely dry, as if it belonged someplace hellishly hot and not this winter place covered in snow.

In the third car, she found a sight similar to the one in the second, where she’d left Miss Clay and Mrs. Butterfield—except here, most of the faces pressed to the windows belonged to men in uniforms. Horatio Korman stood against the far wall alone, arms folded. He glanced up at Mercy when she came blasting in, accompanied by the weather, and he gave her a frown that told her to shut the door, already.

She did so and approached him, cheeks flushed from even that brief exposure, and hands shaking despite her gloves. She said, “Is it them, do you think?”

“Yeah, I think it is.”

“Can they catch us?” she asked for what must’ve been the hundredth time.

He sucked on his lower lip, or on the gobbet of tobacco he undoubtedly stored within it. Then he reached for a window, lowered it, and spit quickly before closing it again. His mustache ruffled and his hat pushed back by the wind, he shook his head slowly and said, “Not ‘can they?’ but ‘when will they?’ We’re less than five miles from the pass, and once we’re in, it’s cliff face straight up and down, on both sides of the rails—an expanse that runs maybe a quarter mile wide, with about twelve sets of tracks running through it.”

Mercy tried to imagine it: a frozen corridor like a tremendous wagon track in the snow, with no way up or out to the left or right, no way to back up and go around, and a race to get through to the other side.