There was no point in returning to the museum immediately. After the disastrous matinee performance, the evening show would be canceled, and no one was eager to return to talk of the museum shutting down.

Instead, they rode the subways aimlessly for a while, barreling through the hot tunnels and emerging onto streets sizzling in the sun. Thomas allowed himself to relax, allowed himself to forget temporarily about Rattigan in Chicago and poor Manfred Richstone and the unknown killer here. They ended up at the Fulton Fish Market, where they stared for a while at the endless wooden stalls and the rainbow-array of seafood, and tattooed men loading cargo on the docks, and the East River flashing like a coin in the sun.

From there, they made their way toward Chinatown, inching forward with the densely packed crowd, navigating crates stacked with salted cod and seaweed, dried eels and fresh shrimp, the pavement puddled with trampled fishtails and old water. Pippa held her nose and complained the whole way, while Max poked at the live frogs and watched them wriggle away in their barrels.

By then, Thomas was starving. He turned around to suggest to the group that they stop and find someplace to eat, when a meaty kid wearing a dark hat pulled low barreled into him. Thomas stumbled backward, nearly upsetting a large crate of blue crabs, before the boy helped him regain his feet. The shopkeeper, a small, wrinkled Chinese woman, released a string of curses in his direction.

“Sorry,” the boy mumbled, before lurching off.

“You all right?” Sam said, carefully squeezing through the crowd.

“Yeah.” Thomas rubbed his chest, where the boy’s elbow had jabbed him. Fortunately, the spot was several inches away from his puncture wound, which had yet to fully heal. “I’m sure he didn’t mean it.”

Pippa went suddenly pale. She seized Thomas’s arms, startling him so badly he nearly went backward into the crabs again. “Where’s your wallet?”

“My . . . ?” But even before his hand went to his pocket and found it empty, Thomas knew. The boy. The “accidental” shove. One hand helping Thomas to his feet, while the other hand dipped into his pocket.

“He took your wallet,” Pippa said.

“That snake,” Max spat out, even though, Thomas knew, she had picked hundreds of pockets.

“Come on.” Sam plunged into the crowd. “There’s still time to catch him.”

Thomas started to move. But the crowd was too dense, too uniform. Even Thomas, who was used to squeezing and bending through the smallest spaces, found it difficult to move quickly, and Sam, Max, and Pippa were soon left behind, borne back by endless waves of people. Hundreds of faces, thousands of bodies, like an enormous human jigsaw puzzle. The boy might have gone anywhere, in any direction, or turned off the street at any time.

Thomas fought a rising sense of frustration and anger. He didn’t so much care about the wallet, a battered leather thing that had, according to Mr. Dumfrey, once belonged to Al Capone and sported a little hole supposedly made by a tommy gun bullet, and he had no more than fifty cents folded into its lining. But his wallet also contained a photograph of Dumfrey holding a baby Thomas on his lap, sitting on the stairs of the museum and squinting into the sun; an Indian arrowhead given Thomas by Hugo the Elephant Man, who had left the museum earlier that spring to marry Phoebe the Fat Lady, and a note written to Thomas from Freckles on his birthday last year. You’re one year older—don’t let it bend you out of shape!

In Thomas’s mind, the contents of the wallet proved that he wasn’t an orphan—not really. The people at the museum were his family.

Thomas searched the crowd for the floppy brown hat. But from his position, he saw nothing but a dense network of backs and shoulders, a sludgy procession of sweating bodies, oozing down the street like mud through a narrow canyon. He needed a better vantage point. Darting to the side of the street, he hopped up on a pickle barrel—ignoring yet another angry shopkeeper—and, with one neat handspring, catapulted himself from metal arm to awning. From there, it was a single leap to one of the fire escapes stitched neatly up the side of the tenement buildings.

He squatted on one of the landings, catching his breath, scanning the crowd trudging below him on Canal Street. Old men, fat men; women with powdered cheeks and rouged lips; children squawking and bawling or grinning fat-cheeked smiles. He saw Max, elbowing people out of the way, and Sam following behind her, careful not to touch anyone; and Pippa floundering to keep up, as if she were riding in the wake of an enormous ship. Sweat trickled down his forehead and he swiped it away impatiently.

There! He caught a glimpse of the floppy brown hat just as it, and the boy, turned right on Mott Street.

“Max! Sam! Pippa!” Thomas waved his arms frantically to attract their attention. They looked up, staring at him gape-jawed. He didn’t have time to explain how he had ended up on a fire escape high above the street. “That way!” he cried out, pointing to the place the boy had just vanished. “He’s heading south on Mott Street!”

Max, Sam, and Pippa plunged gamely on through the crowd. Thomas nearly vaulted over the railing—two quick jumps and a slide down the awning would bring him back to street level—but then thought better of it. He’d never catch up to the thief, not that way. Instead, he turned and threw himself at the nearest window. Locked. Inside, he could see a woman with the puckered face of a wizened apple knitting in a rocking chair, gazing at him impassively, as if it were totally normal to see young boys on her fire escape, attempting to gain admittance to her apartment.

Thomas sprinted up the next set of stairs. Here, he had more luck. The window that gave onto the fire escape was open a few inches, allowing Thomas to shimmy through it. He dropped into the kitchen, landing lightly on his feet directly in front of a young woman wearing an apron, holding a large plate of slightly burned sausages. She gaped at him. A small, animal sound began working its way out of her throat.

“Don’t be afraid,” he said quickly. “I’m just passing through.”

She shut her mouth so hard, so fast, he heard her jaw click.

Thomas dashed through a narrow hallway and found himself in a cluttered living room. In one of the many overstuffed armchairs, an enormously fat man wearing a stained white undershirt was listening to the radio and drinking a soda. The man didn’t even look up.

“Martha, can you grab me another soda?” he grunted as Thomas squeezed behind him.

Thomas pinched his throat and made his voice a falsetto. “Right away, sweetie,” he trilled, and kept moving.

Down another hallway, where the wallpaper was peeling in strips; through a tiny bedroom and an even smaller bathroom; into a second bedroom, fitted with nothing but a washstand and a narrow cot, in which an old lady was (thankfully) asleep. Thomas eased onto the bed, careful not to disturb her, and heaved open the window. Wriggling through it, this time on his stomach, he tumbled headfirst onto yet another fire escape.

Thomas’s gamble had paid off: the boy with the floppy hat was just crossing onto Pell Street, dodging a dizzying grid of cars and pull-carts. As Thomas watched, he slipped into a narrow gap between buildings. Thomas pounded down the fire escape, taking the last ten-foot drop easily, rebounding off a fabric cart and dashing across the street. Car horns blared, and tires screeched on the asphalt.

He reached the alley just as Sam, Pippa, and Max finally rounded the corner of Mulberry Street, shouting his name. But he didn’t stop. The boy in the floppy hat had almost reached the chain-link fence at the end of the alley, and Thomas knew if he didn’t catch up, the boy would soon disappear into the maze of streets and buildings on the other side.

On one side of the alley, trash cans were lined up for collection, clustered like mushrooms after a rain. Thomas jumped and dashed across them, banging and clattering, using the lids as footstools. His chest ached and his breath was rasping in his throat. The blood was pounding in his ears, transforming the noise of the street—traffic and horns, shouts and catcalls—into a distant rhythm. He was getting closer. Closer.

The boy reached the fence as Thomas vaulted off the final trash can. For one second, he was in the air; then he was swinging from a laundry line stretched tight across the narrow gap between buildings, as a red shirt and a pair of frilly underwear came flapping down around his ears; and then he was dropping, tumbling onto the boy’s back. The boy cursed, releasing his hold on the fence. Together they rolled, and Thomas felt his cheek hit the pavement and tasted dirt. The boy elbowed him roughly in the chest, and Thomas saw stars of pain: it was exactly the spot where he’d been stabbed a few days earlier. Thomas rolled onto his back, gasping, and the boy sprang to his feet again, hatless, and swung himself up onto the fence like an overgrown spider.

Thomas struggled to sit up.

“Thomas! Stay down!”

Thomas turned and saw Max positioned at the end of the alley, one arm cocked, knife raised. There was a whoosh of air. The boy yelped and nearly fell, catching himself at the last minute. The point of the knife was buried in the thick rubber sole of his right shoe. Even as Thomas pushed himself to his feet, however, the boy was off again, kicking off his shoe and hauling himself toward the top of the fence, now with one dirty polka-dot sock exposed.

Thomas reached the fence next. Max, Pippa, and Sam weren’t far behind. The chain link swayed under their combined weight as they clawed for the top.

They jumped together, landing almost simultaneously on the far side of the fence.

“Stop where you are!” someone shouted.

Thomas looked up. The boy—who was now hatless, revealing a thatch of mud-brown hair, and a face so crowded with dirt and freckles, it was impossible to tell one from the other—was standing in the shadows underneath a makeshift shelter, a half-collapsed shed in a barren courtyard behind an abandoned building. He wasn’t alone. From the shadows, several other boys emerged, grim and determined, hands clenched into fists as though preparing for a fight. All of them were dirty, many of them shoeless, and each of them had the desperate look of a trapped animal. They began to circle, pressing closer, like a pack of wolves around their prey.

“Sam?” Thomas whispered.

“Yeah?” Sam was very white. More and more kids were emerging from the shed: six, seven, eight of them, now.

“You know that thing you do with your fists? The one that makes people run away?”

Sam nodded.

Thomas swallowed. “I hope you’ve been practicing.”

There was a long second of ragged tension, like the queasy few moments right before a thunderstorm, when no one moved. Then everything unfroze. Three boys rushed Sam at once. Pippa screamed. Thomas saw a jagged bottle flying in his direction, and barely managed to duck.

Then a familiar voice was shouting: “Hey! Lay off! Leave ’em alone!”

Another boy was shoving his way through the crowd out of the shadows, a battered news cap pulled low over his eyes. His pants were torn at the knees, and his face was streaked with dirt. But there was no mistaking his snub nose, smattering of freckles, and bright green eyes.

“Chubby?” Thomas said.

Chubby smiled shyly. “Heya, Tom,” he said.