Thomas should have known that when Pippa said she had a plan, what she meant was that she had a plan for him—which is why he now found himself squeezed into a shoebox-size space between an air duct and a nest of rusted iron pipes.

It was hot, airless, and cramped; he was fighting a sneeze that had begun as a tickle in his nose but now seemed to have him by the throat. Carefully, he extended one hand through the network of pipes and found purchase on an old iron knob. Holding his breath, flattening his lungs, trying to picture himself as a pancake, he pulled himself through a narrow gap between pipes, and at last found himself pressed against the iron grille, roughly level with the floor, looking out over the forbidden, the absolutely off-limits, chambers of Potts.

The performers all lived together in the attic, their respective sleeping spaces separated by a complex network of old junk that had drifted there over the years, like an upward-falling snow. Plaster statues, old desks, folding screens, and upturned mattresses—all were arranged for privacy in a labyrinthine formation bewildering to anyone who was a stranger to the museum.

Only Mrs. Cobble, Miss Fitch, Potts, and Dumfrey had their own quarters. Mrs. Cobble slept on the first floor, in a room accessible from the Special Exhibits Hall and directly above the kitchen, from which she claimed to be able to keep track of the larder even while asleep (a claim disproved by frequent midnight raids on the kitchen). Miss Fitch slept in the props and costume department on the second floor, in a bed allegedly once owned by a famous murderess and still sporting a bloodstain on its wood frame. Mr. Dumfrey maintained his bedroom behind his office on the third floor.

And Potts—the miserable, evil-smelling, bad-tempered Potts—had chosen to make his home in the basement. No one ever dared to disturb him down here, and Potts even kept his door locked, as if to double-guarantee against snoops and intruders.

Carefully Thomas threaded his fingers through the grate and pushed until he felt it give. With a small pop, the grate released. He set it aside on the floor while he wriggled through the narrow opening, head and shoulders first, emerging from the wall like a worm emerging from damp ground.

He was in. Thomas straightened up. All was silent, except for a quiet dripping sound. At last, Thomas’s heartbeat slowed, and the sneeze that had been crawling through his nasal passages had gone back to wherever unsneezed sneezes go.

It was dark in the room and smelled like old tobacco and rotten milk. Thomas fumbled for a light switch on the wall. A single wire-encased bulb flickered to life in the ceiling, illuminating a narrow, windowless space, walls bubbling with moisture, and a rusted old sink in the corner, which Thomas identified as the source of the dripping. The room was heaped with clothes and junk, littered with old mugs in which suspicious liquid was developing thin films of mold, filled with all sorts of broken, useless, ugly things—a mirror so cracked it split Thomas’s reflection into a hundred tiny Thom-ases; a stool with only a single leg, overturned; a razor coated with cream and hair.

“Now what?” Thomas said to himself in a whisper. Pippa had sworn Potts would be out of the museum for hours, but still Thomas felt the hairs on his neck standing up, as if someone were watching him, concealed in a corner. To calm down, he did calculations in his head. The perimeter of Potts’s room was 56 feet, and the area 192 feet. The density of the laundry piled at the foot of his bed was roughly 24 socks per square trouser. . . .

Look for proof, Pippa had told him—but what kind of proof, she couldn’t say. It was extremely improbable that Potts had the shrunken head just stuffed into his bureau with his socks, especially since the money in his pocket suggested he had already sold it. But maybe there was evidence the head had been here and then moved—or maybe the payment was merely a portion of the money, like an advance, and Potts was concealing the head among his things before he deemed it safe to move.

Thomas picked carefully through the dirty laundry strewn across the mattress, moved aside furniture, checked every corner and cubbyhole. He found several pairs of dice, one of them weighted, and a stack of well-worn playing cards.

Every surface was littered with matchbooks from various restaurants, most of them with names like the Rusty Nail and Pig & Whistle. He found a piece of paper bearing a handwritten Brooklyn address that he initially thought might be important, until he saw that it was labeled Anderson’s Delights. He assumed it was another restaurant.

Other than that, nothing. Not a thing to suggest that Potts had been involved in the theft. No incriminating messages, no guilty confessions.

Thomas was just shutting the bottom drawer of the bureau when he heard heavy footsteps in the hall. He froze. The feet stopped just outside the door.

Potts.

A key turned in the lock.

There was no time to make it back to the grate and into the safety of the wall. Thomas looked around frantically for a hiding place—and then just as the door began to scrape open, hurled himself into the bottom drawer of the misshapen bureau, managing through a series of wiggles and shoves to get it closed. He squeezed himself into a ball, choking on the smell of old socks. Knees to eyeballs, feet to butt, bending, folding, an origami figure of a boy.

Flat as a pancake. Small as a shoe.

He heard Potts enter—smelled him, too, the stink of tobacco and unwashed denim that preceded Potts everywhere like a forward-drifting cloud. Thomas’s heart was hammering so loudly, he was sure Potts would hear it. He wished he could flatten his heart, too, and stop it from pounding like a drum.

Potts crossed directly toward him—without hesitation. Thomas’s mouth went dry as dust.

The bureau rattled; wood scraped on wood, as Potts began rummaging through the drawers.

“Where’d I put the blasted thing?” Potts muttered. He closed the first drawer. Moved onto the second. Sweat pooled on Thomas’s forehead. His legs and knees were already aching. Any second now . . .

Then Potts gave a grunt of satisfaction. Whatever he was looking for, he had found it.

Thomas was safe.

Potts began to cross back toward the door, and Thomas allowed himself to relax, just slightly. Then there was the bang of metal and Potts cursed.

“What in the . . . ?”

Thomas’s stomach dropped out through his feet. The grille. He had forgotten to replace it. Now Potts would know that Thomas had been in his room.

Sure enough, Potts had stopped moving. The silence was still, electric, agonizing. It seemed to last forever. Then Thomas heard a sharp sniffing. Potts was trying to smell him out, the way a dog would.

“Come out, come out, wherever you are,” Potts singsonged. “Come out, you little worm. I know you’re in here.”

Thomas couldn’t have moved if he wanted to. He was terrified into utter stillness. Go away, he thought. Please just go away.

Potts began shoving aside furniture. Thomas’s whole body went white-hot with fear when Potts drew close to the bureau. Potts shoved the bureau away from the wall with a cry of “Aha!” But he didn’t think of opening the bottom drawer, where Thomas hid in thick and filthy-smelling darkness, sweating against the splinters.

And then it happened.

The sneeze—the sneeze Thomas had repressed and swallowed until it returned to wherever unsneezed sneezes go—came roaring back. It blew up his throat and exploded into his nasal passages. It reverberated through his whole body. There was no stopping it. It was a storm, a force—and when Thomas sneezed, the whole bureau sneezed, too, and shot out its bottom drawer like a giant wooden nose expelling snot.

And even as the echoes of the sneeze were still hanging in the air, as Thomas was wiping his nose with the back of his hand, shaken, exhausted from the force of that superhuman sneeze—even then, the looming shadow of Potts spread over him, and the stink of tobacco grew stronger.

“There’s the little worm,” Potts said, showing off all his rotten teeth. And he bent over and plucked Thomas up with one meaty hand.