The rain in Chicago didn't fall so much as it materialized from the air, a fine grey mist that coated everything in a film of perpetual dampness. Jack Malone stood under the awning of a closed newsstand on State Street and watched it turn the sidewalks into mirrors that reflected the neon signs of bars that were already full and the neon signs of bars that were about to open. He had been standing there for twenty minutes, smoking cigarettes that cost twelve cents a pack and thinking about the last three years of his life, which had been a series of mistakes that looked like opportunities until they didn't.

He was thirty-one, which meant he had spent eleven years since the war thinking he was a man who knew what he was doing. The war had been over for five years, but Jack still woke some nights with the sound of artillery in his ears and the smell of mud and cordite in his nose. He had come home from France with a medal he didn't want and a paycheck that ran out in three months and a skill set that consisted of killing people and driving trucks, neither of which was in high demand in peacetime Chicago.

The first mistake had been taking the job with O'Malley's crew. Patrick O'Malley was a small man with a big voice and an even bigger ego, the kind of man who thought the Prohibition era was his personal invitation to become a king. Jack had been hired as a driver, which sounded simple enough: pick up the whiskey, drop off the whiskey, don't get caught. The pay was good. The work was steady. And Jack needed steady.

The second mistake had been trusting O'Malley. The third mistake had been trusting Sal Benedetto, the crew's enforcer, who had a face like a clenched fist and a laugh that sounded like gravel in a blender. The fourth mistake had been getting involved in something that wasn't about whiskey at all.

It started with a package. A wooden crate, no bigger than a suitcase, delivered to a warehouse on the South Side. O'Malley told Jack to drive it to Milwaukee. Simple enough. Except when Jack opened the crate in the back of the truck, he found not bottles of whiskey but three Thompson submachine guns and a stack of documents stamped with the seal of the U.S. Treasury Department.

He should have turned around. He should have driven straight to the nearest police station. Instead, he drove to Milwaukee, delivered the crate, and collected fifty dollars in crisp bills that smelled of someone else's sweat.

That was October 1925. It was the first of many deliveries. Each one was slightly more dangerous than the last. The packages grew larger. The destinations grew more remote. The money grew larger. And Jack, who had been a good soldier and a mediocre driver and a man who liked steady work, found himself climbing a ladder whose top rung he couldn't see because the fog was too thick.

The turning point came in the spring of 1926. O'Malley gave him a package to deliver to a man named Voss, who lived in a house on the lakefront that looked like a European castle had been dropped into the middle of Illinois and didn't know what to do with itself. Voss was a German who had come to America before the war and never left, carrying with him the kind of accent that made people lean forward to hear him and the kind of eyes that made people lean back.

Voss received the package in a room that was lined with books—real books, not the paperbacks that lined O'Malley's office shelves—and invited Jack to sit down.

"You're a soldier," Voss said. It wasn't a question.

"I served."

"In France?"

"Yes, sir."

Voss nodded slowly. "I served in Germany. Same war, different side. We both came back to find that the people who sent us there were richer than before."

Jack said nothing. The rain tapped against the window like a finger asking to be let in.

"I have a proposition for you," Voss continued. "Not with O'Malley. With me. O'Malley is a street thug with a government contract. I am a man who understands that the world is about to change, and the men who understand that first will be the men who shape it."

"What kind of change?"

Voss smiled, and it was not a nice smile. "The kind that makes Prohibition look like a children's game."

Jack should have left. He should have walked out of that castle on the lake, driven back to his flophouse on West Madison, packed his one suitcase, and caught a bus to anywhere that wasn't Chicago.

He didn't.

The proposition was simple: Voss wanted Jack to use his driving skills and his military training to transport something much larger and much more dangerous than Thompson submachine guns. Something that would make O'Malley's entire operation look like a candy store.

Jack asked what it was.

Voss opened a safe behind a painting of a Prussian general and took out a single sheet of paper. On it was a diagram of a device that looked like a cylinder made of brass and glass, with labels in German that Jack couldn't read but could feel the danger of, the way you feel the danger of a snake before you see its head.

"This," Voss said, "is not a weapon. Not yet. It is a key. And the door it opens is one that the world is not ready for."

Jack stared at the diagram. He thought of the artillery in France, of the mud and the blood and the boys who had died screaming in trenches that no one would ever remember by name. He thought of O'Malley's fat wallet and Sal Benedetto's gravel laugh and the fifty-dollar bills that smelled of someone else's sweat.

"What's on the other side of the door?" he asked.

Voss closed the safe. "That, Mr. Malone, is what you are about to find out."

Jack drove back to his flophouse in the rain. He sat on the edge of his bed and stared at the ceiling, where a water stain looked like a face he almost recognized. He thought about turning around. He thought about the medal on his wall that he had never taken down. He thought about the green ledger of his life, where every line was a mistake that looked like an opportunity until it wasn't.

In the morning, he would make his choice. In the morning, the rain would still be falling. In the morning, Chicago would still be a city of mirrors reflecting neon signs in wet sidewalks.

But not yet. Not yet.