She didn’t dare look over her shoulder. She waited at an intersection because she had to, and when a glass-windowed cabriolet went lumbering by, she scanned its reflections for the men behind her and spotted one of them. Only one? Maybe the vehicle passed too quickly, and she’d missed the other. Or maybe the other man had broken off from the direct chase, and was circling around from a new direction.

While she waited for the traffic director to give her leave, her mind raced.

How much farther to the station? No more than a few blocks, surely. Any available shortcuts? She didn’t know the city well enough to say for certain. She swallowed hard and, when the traffic director waved her across the road, she continued onward, still pretending that nothing was wrong, no one was behind her, and hers was an ordinary errand to the train station—no different from a thousand other ordinary errands performed every day.

Under pretense of stopping to adjust her shoe, she surreptitiously checked and confirmed that one fellow was still on her tail—the fact of this never more obvious than when he realized she’d paused … and he did likewise, investigating a news stand with sudden, intense interest.

“Maybe he’s an amateur, or a Baldwin after all,” Maria griped as she straightened up and resumed her path.

A sign posted beside the road pointed an arrow at the station, noting that she was still over a mile away; so, her recollection of how the city worked had been foggy indeed. She swore under her breath. A mile was a long way to run, and a long way to evade anybody. It gave the men plenty of time to close in on her, cut her off, and do whatever it was they planned to do.

And she still didn’t see the second fellow. He could be anywhere.

However, she did see one of the new electric streetcars clattering toward her. It wasn’t pointed in the right direction, except that right now the right direction amounted to “anywhere else but here.”

Chicago did not yet have these electric street lines, so she had no experience with such things. She sized up the elongated, open-air car. It didn’t look too complicated. When the painted trolley came close enough for her to touch it, she reached out and grabbed one of the vertical poles along its exterior, like she’d seen people do in other places during her travels.

It didn’t move quickly, but it moved determinedly, yanking her off her feet with exactly the precision and insistence she’d hoped for. She grunted with surprise, then smiled as her feet found a step. Tightening her fingers around the bar, she shielded her eyes from the sun shimmering off the frosty city. She spied the first man at the curb behind her, visibly aggravated that he’d arrived too late to join her.

Moments later she saw the second man hunting down a side street. He did not see her hanging off the side of the streetcar like she did this every day, like any of the other passengers who took such a casual attitude toward their transportation and bodily safety.

When she felt confident that she was unaccompanied, at least temporarily, she waited for the next stop and asked the driver if he could help her reach the train station.

The driver delivered the gentle admonition that she’d gone the wrong way, and she pretended she hadn’t known—because every man liked to be a hero, or at least enjoyed being of service to a lady in distress. And why deny the nice gentleman a warm feeling of helpfulness?

She finally made the right connection, and soon she reached the station, bought her ticket to Fort Chattanooga, and positioned herself comfortably on the last train of the day to the fort as the train prepared to depart.

Maria sat next to the window but turned her face away from it, in case anyone had caught up to her. She had no doubt that whoever’d sent the two men would learn her location soon enough, but there was no reason to make it easy for them.

The train lurched forward and found its rhythm.

And now she had hours before her with nothing else to do but familiarize herself with the nurse’s missives.

The pages were difficult to skim, due largely to the questionable handwriting of the woman who’d composed them. At a glance Maria could see that the nurse had never enjoyed more than a few years of formal schooling, as the earnest, rounded letters showed the charming diligence of a child’s hard-practiced lessons. But there was nothing charming or childlike about the message these shaky letters conveyed.

She checked the most recent letters and saw that the handwriting improved over the course of the correspondence, practice making something closer to perfect. Even so, the early pages were slow going, and the rollicking track of the train gave Maria a case of motion sickness that almost made her quit trying; surely it would be easier to finish the reading from a stationary location.

But a phrase leaped out at her. She drew the page in question up close to her face.

“… if you could hold him still for long enough, a doctor would pronounce him dead.”

Her attention now more fully engaged, she made the effort to peruse the entire section from whence the eye-catching line emerged.

I have now seen four cases here in the underground, and they all go the same: First, the victim breathes up some gas—usually because a mask springs a leak, or isn’t fixed good on his face in the first place. But sometimes it happens because the mask gets knocked off, or one of the tunnels isn’t sealed up as good as everybody thought. Doesn’t matter how it gets inside, it always goes the same.

After a man breathes it, his nose starts running with yellow mucus, and the mucus is sometimes bloody. Sores break out around his eyes, ears, and mouth. It looks like the gas is eating him up from the inside out. Then the heart stops, the pulse quits. No more spit or tears, and the skin around his eyes turns yellow. He starts panting, and it sounds like his lungs are being chewed up into rags. You will never forget what it sounds like, when he breathes. For that matter, if it weren’t for that breathing, you’d never know he was alive. Everything else about his body has done stopped, like he’s been killed by a plague. If you could hold him still for long enough, a doctor would pronounce him dead.

But he won’t stop moving like a polite dead man. Just when he ought to lie down and take a proper Christian burial, that’s when he starts running around, trying to bite people.

Sometimes it happens quicker than other times, from start to finish. The people I talked to say it’s because the gas is very heavy, and it collects thicker in some places than in others. It moves like a real thick liquid, like a syrup you can hardly see.

Maria sat up straight and frowned at the paper. As promised by Captain Sally, the text described a poisonous gas, and it definitely sounded like the walking plague. In fact, the nurse had used both of those words, fairly close together: “walking” and “plague.”

She kept reading.

Once a man’s been bit by a rotter, treatment is pretty much a race against the clock. Whatever gets bit has to get cut off. The bite causes a festering that moves like blood poisoning through a body, or like septic rot, but faster. If a finger gets bit, you’d better cut off the hand. If a hand gets bit, you’d better take the whole arm. If the amputations don’t happen in time, the patient will die within a day or two. I am told that a patient who dies from a bite will not start walking like a rotter, and so far this seems to be true. But I only seen it on three occasions so far, and that is not enough for me to say for certain.

“Gruesome,” Maria murmured with fascination. She flipped to the next page.

Nobody knows how long the rotters will keep moving, but the oldest ones have been kicking around for about fifteen years, by everybody’s best guess. The real old ones are raggedy now, and when you see them, you wonder how they manage to move at all. Most of the skin has rotted off, and the muscles are hardly more than strings. I hear they take nourishment from what they eat, but since their blood don’t flow I’m not sure how that’s possible. And since there is not much to eat inside the walls, it makes me wonder. I guess they have been eating the Doornails or the Station men, but I am told that, these days, it is unusual for more than half a dozen men to die that way in a year. For the most part, people have figured out how to live here without getting eaten. But those first few years after the wall went up, a whole bunch of people got killed by the gas and the rotters. Mostly I think people were trying to get inside the city and either loot it or get back the stuff they’d left behind. And I’d like to tell you that it was a stupid thing for them to do, but until they did it, nobody knew what would happen to them. Now everybody knows.

I know what happens to the men who do the gas-drug, too, but no one will listen to me. I’ve tried to tell people, and to ask for help. I used letters and the taps as best I could, but no one from the Dreadnought has answered—though my friend Angeline says I should try the Texas Ranger again. His name was Horatio Korman, and if you can reach him, he may be of some help to you. You might also ask after the captain on the train, a man by name of MacGruder. I have got to say he conducted himself like a hero, but I doubt you’ll have any means of finding that one, as he’s someplace up north. I am told there’s also an airman named Croggon Hainey who might serve as witness, but him being colored and being a pirate, he’s not likely to be believed.

Maria was startled to see the air pirate’s name. Croggon Hainey was the captain of a ship named the Free Crow (though it was briefly called Clementine). It had played a role in her first case as a Pinkerton agent, the one she’d been reassured had been resolved to everyone’s satisfaction … including the pirate’s.

“Small world,” she said under her breath.

She flipped back to the top of the stack, scanning for a location or an address. Nestled between two stacks of notes tied with twine, Maria found a brown paper envelope with the information she hunted.

The name on the envelope was “Venita Lynch,” at odds with the reports themselves, which were usually signed “Mercy.” “Seattle,” she read aloud from the return address, wondering if she was pronouncing it right. “The Washington Territories.” She knew where Washington was, at any rate. It was as far west and north as you could go, without getting very, very wet … or wandering into Canada. Upon inspection of the postal mark, she saw that the envelope had not been mailed from Seattle at all, but from Tacoma. “Where the transcontinental line ends,” she mused. The two cities must not be far apart.