The cafeteria was even noisier than usual, three days later—so loud it was almost giving Cody a headache. In addition to the usual lunchtime pandemonium of trays clattering and coins clanging into vending machines and paper bags rustling, it seemed every kid in the place was yakking away at a decibel level that rivaled a Justin Bieber concert.

“Let me guess,” Cody said dryly, tossing his lunch bag on the table. “Everyone’s talking about the big food drive to help the homeless.”

Willie looked around and shrugged. “You gotta admit it’s pretty exciting,” he said. “It’s not every day you have the police crawling all over the place and students being questioned.”

Cody nodded. Willie was right—you couldn’t blame the kids. “The Great York Middle Crime Wave,” as it had been dubbed, was all anyone was talking about.

Even though there had been a few thefts in previous weeks, most of the school considered the start of the crime wave to be the day Cody and Nicky Evans had reported their cell phones missing in gym class. Later that same day, a girl in eighth grade had reported that her cell had been stolen from her locker.

By the next morning, a computer from the computer lab was missing, and two teachers had reported having their wallets stolen from their handbags. And just the day before, Ms. Wratched had arrived at school early in the morning, snapped on the lights to her classroom in the science wing, and let out a loud, piercing scream. At first her fellow teachers had ignored her, thinking she’d simply seen another mouse scurrying across the floor. That sight had become rather commonplace with all the construction work going on outside. It was disrupting the habitat of critters big and small and causing them to seek shelter elsewhere.

When Ms. Wratched’s fellow teachers finally decided to investigate, they found her standing in the front of the room with a shocked expression, staring at a gaping space on the wall where a flat-screen TV had been. Now all that remained were a few wires dangling forlornly from where the unit had been ripped from the wall.

In addition, at least ten other students had reported their cell phones or iPods stolen in the past few days. In fact, so many were now missing that when a student went to the main office to report a theft, the bored-looking secretary didn’t even look up, but simply pointed to a notebook under a cardboard sign that read: HAD SOMETHING STOLEN? LEAVE YOUR INFO HERE.

Now the entire student body was buzzing about whether the thefts were an “inside job” perpetrated by a York Middle student or students, or whether a nefarious gang of professional thieves had descended on the normally quiet school.

“I’m going with professional thieves,” Willie said now, munching on a cookie. “There’s too much stuff missing. It can’t be just kids.”

Connor snorted and shook his head. “Have you been watching that dumb Ocean’s Thirteen movie again?” he said. “Why would a bunch of slick thieves target our little school? Huh? How much money are they going to get for a computer and a few crappy iPods and cell phones?”

He took an enormous bite of his turkey sandwich and continued. “Even the TV from Ms. Wratched’s room would be small change for your average master thief. He’s not risking ten years in the slammer just for that.”

Now it was Willie’s turn to snort. “Oh,” he said, “listen to the star of Criminal Minds.”

“Make fun all you want,” Connor said. “But it’s true.”

Suddenly, they heard a loud “OOOH! OOOH!” from the far end of the table. Everyone turned to find Marty with his hand raised.

“I have a theory, if you’ll permit me,” Marty said.

Jordy rolled his eyes. “Marty, you don’t need permission to speak here,” he said. “And you don’t have to sound like such a dweeb. Who talks like that? ‘If you’ll permit me’?”

A week earlier, Cody had finally coaxed Marty into leaving the geek table at the back of the cafeteria and sitting with his Orioles teammates. But Marty still seemed in awe of his surroundings and had only recently worked up enough nerve to join the conversations. Most days he preferred to keep his head down, nibbling like a tiny woodland creature at the weird sandwiches he brought for lunch, including the hummus-and-cream-cheese-and-onion sandwich that was now grossing everyone out.

“Okay,” Marty said, looking around and dropping his voice conspiratorially. “I think Connor’s right. I think it’s someone right here in school. He walks among us. He talks like we do. He knows our every move.”

“You make him sound like an alien,” Willie muttered.

“Or an angel. Or a demon,” Jordy said.

Marty smiled, revealing a pasty brown mouthful of gunk and tiny green clumps stuck to his teeth. The other boys winced. Well, Cody thought, now we know the cream cheese had chives in it.

“Oh, no, my friend,” Marty said. “He’s not from another world. Far from it. He’s a living, breathing York Middle student. He might even be sitting in this cafeteria right now. Not at this, um, particular table, of course.”

“Well, that’s a relief,” Jordy said.

“The point is that it’s probably someone we’d never suspect,” Marty continued. “Someone who looks totally innocent. Someone like, I don’t know, Nicky Evans.”

“Nicky Evans stole his own cell phone?” Willie said.

Marty shot him a withering look.

“I’m just using him as an example, Einstein,” he continued. “It’s someone who doesn’t draw attention to himself. But someone who knows where everyone keeps stuff.”

Cody finished his lunch and crumpled his brown bag into a ball, staring pensively at Marty. “You keep saying he,” Cody said. “What if the thief is a girl?”

“Highly unlikely,” Marty said. “Girls are more likely to engage in crimes such as shoplifting and things of that nature. Everybody knows that.”

“There he goes again,” Jordy said. “Sounding like a college professor.”

Connor said, “And how would a girl rip that big TV off the wall in Ms. Wratched’s room? And carry it away? It must’ve weighed fifty pounds.”

Oh, I know a girl who could do that, Cody thought. She’d probably fly through the air, karate kick it off its bracket, and catch it on the way down.

“Mark my words,” said Marty, craning his skinny neck and letting his gaze sweep dramatically from one side of the cafeteria to the other. “The thief walks among us.”

“Then I wish the thief would steal that disgusting sandwich of yours,” Willie said. “It’s making me sick.”