Charlie sat upright in bed with a start. His room was filled with a strange rumbling, whirring noise.

“What’s that?” he exclaimed, turning on the light. The elephants, hippos, lions, and tigers on his wallpaper seemed to stare back at him.

Whirrr-zzz-zzz! The strange sound was coming from outside his room.

Could a guest at Pet Hotel be making all that noise? The hotel was almost full of pet guests, for the first time since it had opened. Charlie and his twin sister, Meg, had given their mom and dad the idea to turn Great-Great-Aunt Saffron’s old hotel into a pet hotel, and now they were taking care of lots of cats and dogs and small furry pets. But as far as Charlie knew, none of them made this kind of noise. It sounded like a giant mechanical bee!

Charlie leaped out of bed and pulled on his paw-print bathrobe. He cautiously opened the door. Two shining lights, like eyes, were coming toward him down the hall.

Tingles ran up and down Charlie’s spine . . . but it was only Meg, shining her pig-shaped flashlight at him. The two spots of light were coming out of its snout!

“What’s making that noise?” Meg asked in a whisper.

“I don’t know,” Charlie murmured. “We’d better check on our guests.”

They tiptoed down the stairs to the second floor, where the cats and dogs slept.

“The noise isn’t as loud down here,” Meg said softly as they peered into the Egyptian room, which had been turned into a special guest room for cats. The statues of pharaohs and the scratching posts in the shape of palm trees made spooky shadows outside the beam of the flashlight. Marmalade was licking her paws and washing behind her ears, and Oreo was stalking a toy mouse. Ginger, Mabel, Skittles, and Ollie were curled up, fast asleep.

“Cats are the best pets ever.” Charlie sighed.

“You’ll have your own soon,” Meg whispered.

“Very soon!” Charlie grinned. Woody, one of the kittens who had recently been born at Pet Hotel, would be old enough to leave his mother and come back this week! Yesterday, Charlie had helped Mom and Dad set up a brand-new cat basket and litter tray for Woody in the corner of the kitchen. He’d spent all the allowance he’d been saving on kitty toys. Charlie couldn’t wait for Woody to come and be his very own pet!

At the other end of the hallway, four of the five dogs staying in the forest room were also snoozing peacefully. Meg shone her flashlight around the dark room. The trees on the wallpaper made it look like a peaceful forest. Affie the Afghan hound and Judy the Old English sheepdog were twitching as they ran in their sleep. Chico the Chihuahua and Amber the Lab were snoring loudly.

“Daisy’s awake!” Meg pointed to the West Highland terrier, a frequent guest at Pet Hotel. She had her head tilted to one side as she listened carefully to the strange noise.

“Woof!” Daisy barked softly when she saw the twins.

“Shhhh!” Meg crept into the room and put her hand between the bars of Daisy’s pen to soothe her. She didn’t want Daisy to wake up the rest of the dogs! If she started barking, that would wake Mom and Dad and Saffron — and Meg’s own puppy, Buster, who slept in his basket downstairs in the kitchen. Daisy licked Meg’s hand and trotted back to her bed. Meg joined Charlie, who was creeping silently down the hall.

Zzz-zzz-whirrr . . .

It was hard to figure out where the noise was coming from!

Charlie stopped near the tiny dumbwaiter and put his ear to the hatch.

“It’s definitely louder upstairs,” he told Meg. “Let’s check the guest room in the attic!”

“But there are only little furry animals up there,” Meg said. “They’re usually so quiet.”

The twins tiptoed up the stairs. Charlie opened the door to the old playroom that had been painted to look like a meadow. It was bathed in silvery light from the full moon outside. The twins could see that, in the twelve hutches around the room, all the little animal guests were wide awake! Many of the hutches had more than one pet inside, since the guests had arrived in groups of two or three. The five rabbits were hopping around, the eight gerbils were gnawing at their cereal bars, and the six guinea pigs made whistling noises as Meg and Charlie entered the room.

Whirrr-zzz-zzz . . .

“It’s coming from that corner!” Charlie exclaimed, pointing.

They tiptoed across the playroom and stopped by the multistory hamster pen.

“It’s Bluebell, Tulip, and Sweet Pea!” Meg gasped, pointing to the three dwarf hamsters who had arrived at the hotel earlier that day. They were running around and around on their exercise wheels, making them go so fast that their little feet were a blur.

Charlie and Meg grinned at each other. Pet Hotel’s smallest guests were the ones making the biggest noise!