Joe gulped. “Um . . . well, you see, sir, I spotted a mouse in the hallway, and it ran under your door. I knocked, but you weren’t in, so I decided to come in and try to catch it . . . But I think it must have eaten your lunch.”

Mr. Hill did not say a word.

Joe could tell that the principal was not in the mood for listening to tall tales. “Honestly, sir, it’s true,” he said weakly.

Mr. Hill crossed his arms, unimpressed. “I was only gone for five minutes, and even if there was a small rodent in my office, which I very much doubt, it couldn’t eat an entire lunch in that time!”

You don’t know what an undead hamster’s capable of! Joe thought gloomily.

Mr. Hill gave Joe a stern look. “Joe Edmunds, taking—or eating—other people’s property is wrong. You can stay inside during recess and think about your behavior!”

Joe shuffled back to the classroom with his head down. “I can’t believe you got me into trouble again!” he muttered to Dumpling, who was stuffed inside his shirt pocket.

“I was only looking for Oliver,” whined the hamster. “When I couldn’t find him I got worried, and you know how hungry I get when I worry.”

Joe rolled his eyes and wished for the hundredth time he’d never set eyes on Uncle Charlie’s amulet.

By lunchtime, the whole school knew about the lunch-box incident. And, to make things worse, Miss Bruce gave Joe extra homework as punishment! Dumpling had nodded off in Joe’s bag, but the lunch bell woke him up, and he started wriggling around impatiently.

“There’s Oliver!” squeaked Dumpling as soon as they went into the cafeteria.

Joe took a deep breath. Talking to Oliver without his friends thinking he’d gone crazy was not going to be easy. Older children never ate lunch with the younger kids. Joe saw Matt and his other friends wave to him from their usual table. He waved back but kept on walking. He went over to where Toby and Oliver were sitting with a couple of other boys and pulled up a chair. “Hi,” he said, feeling very silly.

Toby smiled in surprise.

The other two boys at the table nudged each other. “Is it true you stole Mr. Hill’s lunch?” said one.

“Um . . . sort of,” said Joe, his face turning red.

“Cool!” said Oliver, grinning.

Toby beamed, too.

“Talk to Oliver! Talk to Oliver!” squeaked Dumpling, who was bouncing up and down on top of Joe’s lunch box. “Ask him about me!”

“Yeah, well, I needed a snack to keep me going,” Joe said, pretending to yawn, “because I’m so tired. I was up all night working on my school project about . . . um . . . hamsters.”

Toby looked puzzled. That was the first he’d heard about Joe having a school project.

But Oliver’s face lit up. “Really?”

“Yeah,” said Joe. “I’ve got to do a survey. You know, speak to people who’ve had pet hamsters and ask them all about what food is best, which toys their pets like . . .”

“My hamster, Dumpling, likes his wheel,” said Oliver cheerfully.

Joe frowned. Didn’t Oliver mean that Dumpling used to like his wheel?

“But his favorite toy is definitely his hamster ball,” Oliver added. “I bought it for him last weekend. He loves rolling around my bedroom floor in it!”

“What?” squeaked Dumpling. “He never bought me a ball!”

“Oh, cool,” said Joe. “So you’ve got a pet hamster? Could I ask you some questions about . . . Dumpling?”

Oliver smiled. “Sure! What do you want to know?”

Joe pulled a pencil and a crumpled piece of paper from his bag to take notes. “Well, what about Dumpling’s eating habits? Sometimes hamsters can be a bit greedy.”

“Dumpling definitely is!” said Oliver. “Well, he used to be,” he added, looking a bit worried. “About a week ago he suddenly got skinny, and now he can fit inside his tunnels again.”

“What’s he talking about?” shouted Dumpling. “I’m not skinny, look at me!”

Joe was puzzled. “Really? That sounds a bit odd.”

“Yeah,” said Oliver. “I thought so, too. But Mom says that hamsters often lose weight in the spring.”

“But what about the vacuum cleaner?” Dumpling yelled in frustration.

Joe scratched his nose. Something weird was going on. It sounded like Oliver thought Dumpling was still alive. But how could that be? The hamster Oliver was describing didn’t sound like Dumpling. Unless it was another hamster . . .

That must be it! After the accident, Dumpling had been swapped for a new hamster, without Oliver knowing!

“I’ve been replaced!” bawled Dumpling. “And Oliver doesn’t even know it!”

Joe and the hamster were in the boys’ bathroom, having a quick talk before the end of recess. Since Dumpling had heard the news that he’d been swapped, he had become frantic with worry and started scarfing down everything in sight!

“Stop that!” said Joe, taking a wad of toilet paper out of Dumpling’s mouth. “Look on the bright side—at least Oliver’s not lonely.”

“You’ve got to tell him his hamster’s a fake!” Dumpling wailed.

“How?”

“I don’t know. But you’ve got to do something. You heard Oliver—he’s worried that I’m losing weight. Except it’s not me, it’s a skinny imposter!” And with that, Dumpling snatched up a bar of soap and started chomping. Enormous pink bubbles began to pop out of his nose.

Joe grimaced. He was no hamster expert, but he didn’t think eating soap was good for hamsters—even undead ones!

Then suddenly a nugget of an idea formed in his head. A hamster expert? That was what Oliver needed. Someone who could explain why “Dumpling” had turned skinny! Someone who could go to his house and give him some advice.

“I think I’ve got a plan,” said Joe slowly.

Dumpling stopped chewing.

“I’m going to become a hamster expert. I’m going to learn everything there is to know about them. Then I’ll offer to go around and visit Dumpling to see why he’s losing weight.”

“But Dumpling’s not losing weight, you big dummy!” squealed Dumpling. “I’m Dumpling!”

“Yes, we know that—but Oliver doesn’t!” said Joe, feeling exasperated. “Don’t you see? Once I’m at Oliver’s house I’ll be able to find a way to reveal to him that his hamster’s not you! But first I have to get him to invite me over, which is why I need to pretend to be a hamster expert.”

Dumpling sighed. “That might work. I guess.”

“It will work!” said Joe firmly. It had to work! If it didn’t, he’d be stuck with the whiniest soap-guzzling hamster in the world, forever! And then suddenly Joe remembered something. “Of course! Toby said he was going home with Oliver after school tomorrow—that makes things much easier! I’ll be able to tag along with him.”

Dumpling sniffed miserably. “Hope so.”

Me too! thought Joe wearily.

Luckily for Joe, he had study time in the library last thing on Mondays. He made straight for the reference section, gathered all the hamster books he could find, and then settled down to read.

“Did you know there are over forty different colors of hamsters?” he whispered to Dumpling, who was “working” his way through a book of his own—a very boring one about birds, which actually tasted better than it looked.

“And did you know that baby hamsters are called pups?” Joe added as Matt came over to join him.

Matt made a face when he saw Joe’s book. “What’re you reading about hamsters for?”

Joe shrugged. “Just curious. Hey, did you know most pet hamsters only live until they are about two years old? That’s not very long, is it?”

Dumpling huffed loudly and rolled his eyes. Suddenly, Joe realized that the life span of a hamster probably wasn’t the best thing to mention in Dumpling’s presence. “But they have an incredible sense of smell!” he added quickly.

By the time the bell rang at the end of the day, Joe was well on the way to becoming a full-on hamster bore!

“Hey, guess what,” said Joe as he walked out of school with Matt and Toby. “The smallest hamsters in the world come from Mongolia and they only grow to about two inches long!”

Matt gave him a funny look. “Uh-huh.”

“And did you know that one human year is like twenty-five hamster years?”

“Yeah, yeah, whatever,” said Matt.

“And did you know that hamsters originally come from the Syrian desert, where they build complex systems of deep tunnels?”

Matt puffed out his cheeks. “What is it with you and hamsters today?”

“It’s because of his school project!” said Toby.

Matt frowned. “Huh? What school project?”

Joe quickly changed the topic to video games.

Meanwhile, Dumpling, who was a bit cranky from lack of sleep, spent the entire journey whining about how Oliver’s mom had replaced him. “It’s an outrage!” he squeaked. “Oliver’s probably stuffing the new hamster with treats, trying to make it bigger. We’ve got to tell him what really happened!”

Joe sighed. It was going to be a long night if Dumpling kept acting like this. He was planning to check his mom’s e-mail account again when he got home, to see if Uncle Charlie had replied.

But as soon as he stepped through the front door, he realized his plan would have to wait . . .