SOPHIE SCURRIED ACROSS THE YARD AND DUCKED between the bushes that lined the house. Ethan and Monster joined her. She listened for shouts or alarms, but all she heard was muffled cheers. She guessed someone—maybe Mr. Nightmare and his friends—was watching TV, a football game or a boxing match. They inched along the side of the house. Dropping to her hands and knees, Sophie peeked around the corner into the backyard.

“Who’s that?” Ethan whispered near her shoulder.

Lounging on a chair by the cellar doors was the most enormous man she’d ever seen. He looked like he ate pro wrestlers for breakfast. Muscles bulged from his neck and were threaded with veins. His head was so much narrower than his neck that it looked like it might pop off. The lawn chair sagged underneath him. Maybe he was a friend of Mr. Nightmare’s? One of the cars in front was probably his. “Let’s not find out,” Sophie whispered back.

She retreated, and Ethan and Monster backed up too. Branches scratched her arms. She halted when she bumped into Ethan, who had stopped. “Look,” Monster whispered. He pointed at a basement window, covered in a mat of leaves. “I think I can unlock it.”

Using his tentacles, he fiddled with the window until at last it popped open. Squeezing inside, Monster disappeared into the darkness. “Monster, wait,” Sophie whispered. She flattened onto her stomach next to the window and tried to see in. It was as if the basement had eaten him. She couldn’t see him, or anything else.

After several long seconds, he stuck a tentacle through the window and waved. “Come quickly.”

“Mom and Dad?”

He poked his head out. “No, but you have to see this.”

Ethan helped her pull the window open wider. She wriggled through and then dropped to the ground, landing with a squishing sound on a pile of wet towels. She heard the low buzz of several voices, men and women, their voices blending together into a steady hum— The TV, she thought, except it didn’t sound like a TV anymore.

“This way,” Monster whispered. He tugged on her hand with a tentacle, and she followed him around the corner, past the cellar doors that led to the backyard and the man with all the muscles.

It took a few seconds for her eyes to adjust to the dim, flickering lights. When they did . . . “Whoa,” she breathed. She and Monster were on a balcony—a dark gray concrete slab with a railing that overlooked a sandpit.

Behind her, she heard a soft thump. Ethan. “Where are you?”

“Shh,” both Sophie and Monster said, and Sophie added, “Around the corner.”

Creeping closer to the balcony railing, Sophie looked down into the pit. It was a circle of sand surrounded by a chainlink fence that reached up to where they stood. Outside the fence, below them, were five people on a wooden bench. All of them were watching the empty pit.

“What’s going on?” Sophie whispered. “What are they waiting for?”

“It looks like a gladiator thing. You know, from a video game. ‘Two men enter; one man leaves.’ Or is that from a movie?” Ethan pointed. “Look. Something’s happening.”

A man walked forward. His face was in shadow, but he held up a key. As he displayed it, right, then left, as if he were a magician about to do a trick, the people on the bench cheered.

He pushed a cage up to the door of the sandpit. Sophie couldn’t see what was inside, but the cage rocked from side to side. Climbing onto the top of the cage, the man brandished the key again, and then with a flourish, stuck it into a lock and raised the door.

“This isn’t good,” Monster murmured.

“Behold, Specimen One!” the man cried.

Jumping to his feet, one of the onlookers punched his fists into the air. A woman stamped her feet and whistled, and music suddenly switched on. Heavy drumbeats thudded through the basement, and a guitar wailed as a monster charged out of the cage and into the pit.

Lit by the bulbs overhead, the monster was shriveled and bald. It blinked at the audience with six black eyes that looked like marbles stuck into its bulbous flesh. It had two squat legs and four muscular arms that sprouted out of its back.

“It’s scared,” Monster said.

The monster flexed its four arms and roared, and the watchers cheered louder.

“Or maybe angry,” Monster amended.

Behind the four-armed monster, the cage slammed shut and so did the pit door. Roaring again, the monster pivoted and ran on its feet and knuckles like a gorilla toward the cage door. It grabbed the fence and tried to climb it.

“Correction: very angry.”

The man in charge poked it with a pole, and as he twisted for another jab, Sophie caught a glimpse of his face—Mr. Nightmare.

“You were right,” Ethan said. “He is a good actor.”

The monster swiped at the pole, but Mr. Nightmare pulled it back fast. He poked again, and the monster fell backward onto the sand.

As the onlookers cheered again, Mr. Nightmare sauntered to the pit door. He shoved a second crate in position in front of it. Facing his audience, he raised his fist and the pole into the air, encouraging them to cheer even louder, and then he lifted the door to the second crate. “Specimen Two!” he cried. “Ready your bids!”

A second monster tumbled into the sandpit. This one had an elongated shark’s mouth, a flat face, and spider legs. It was also coated in goo. As it saw the first monster, it hissed.

Sophie leaned forward to see it better. There was something familiar about it . . . and then suddenly she knew why the second monster looked familiar. She’d seen it before: in the somnium. “Monster, I think that’s one of ours. Please, tell me I’m wrong.”

He didn’t say anything.

The first monster spotted the second one. Roaring, it charged.

The second monster opened its mouth and yellow slime spewed out, covering the first monster. The crowd fell silent for half a second, and then roared their approval.

“It is like a gladiator match,” Ethan said.

“With monsters. Our monsters.” Shuddering, Monster wrapped his tentacles around Sophie’s leg. Below them, snarling and snapping, the two monsters in the ring tore at each other while the crowd howled louder.