For a moment, Celia could not move. She almost forgot to breathe. Then she dropped the wagon’s handle and ran toward the end of the long hedge. Her short legs pounded on the turf, and her heart was pounding, too.

If only her parents would come home! But there was no dark blue car coming up the driveway. There was no dust rising on the long dirt road that led from the highway to their mailbox. There was only a tractor in a field, moving slowly.

Celia got to the end of the hedge and peeked around the leafy corner. She did not want to get run down by a mower on the loose.

But the mower was not heading in her direction. It had mown straight down the other side of the hedge, dragging the children behind it. Now it was aiming for the last strip of long grass left on the hill. It hopped across the gravel driveway with hardly a stutter, and picked up speed on the other side, bouncing and clanking down the slope. The tag end of the badminton net flapped like a flag in a stiff breeze.

“STOP!” Abner’s voice was getting hoarse, but he kept yelling anyway. Derek had stumbled, and Tate was trying to pull him to his feet again. Celia couldn’t tell if they were caught in the net or just refusing to let go. But either way, her sister and brothers were being dragged like pull toys.

Celia was not big enough to stop the mower. But once before, she had called to the mower and it had followed her to a new patch of grass. Would it do the same thing again? Maybe she could fool it. If she could get it onto the stone bridge, there would be no grass for it to mow. It would slow down and maybe even stop. It was worth a try.

Celia patted Mr. Bunny’s ears for luck. Then she ran up beside the mower. She smiled and waved. She made her voice sound high and happy. “Come on, Mowey! There’s lots of grass over this way!”

“No—there—isn’t—” Derek said, his words jerking out with every step. “Are—you—nuts?”

“Stay—away!” said Abner, galloping past. “Keep—safe—Celia!”

“But maybe—she’s got—a plan!” Tate’s voice trailed off as they ran.

Celia trotted down to the river’s edge. Reeds were growing there, long and green. She yanked them up and waved them over her head. Then she pointed to the stone bridge and kept on waving. “MOWEY! OVER HERE! LOTS OF GRASS!”

The lawn mower hesitated. It turned toward Celia. Then it gave an eager hop. It tore down the last narrow strip of grass to the river, with Abner, Tate, and Derek bumping and yelling behind.

Celia jumped onto the bridge and ran halfway across. It was going to work! The mower had believed her! “COME ON, MOWEY!” she called. “COME TO THE BRIDGE!”

But the lawn mower did not go to the bridge. It went straight to the river, where the patch of reeds was the thickest. Splash! It leaped into the water and churned ahead, chewing up the reeds. Splash! Splash! Splash! The three children were dragged into the river, one after the other.

Celia did not know what to do. Were her brothers and sister going to drown? Her good idea had just made everything worse.

She looked around in a panic. Where were the grown-ups when she needed them?

And then she did see a grown-up. It was the farmer, on his tractor. He was not far away. Maybe she could get him to help.

Celia’s sandals went thwap thwap thwap across the stone bridge. Mr. Bunny went fuff fuff fuff as he bounced against her side. She ran onto the gravel road and leaped across the ditch. She stumbled through the rows of alfalfa, waving her arms.

But the tractor was bigger than it had looked from a distance. It was very tall, and very loud. It was scary. She could not get close to it. And the farmer was looking the other way.

The tractor roared past. Celia clutched Mr. Bunny to her chest, so hard that his ribbon broke. She turned around, almost afraid to look.

But her brothers and sister were not drowning. The mower was skimming over the water like a motorboat. Water sprayed back from the whirling blades and into the faces of the children floating behind. The droplets shone in the sun to make a rainbow.

Celia ran to the river’s edge. How could Mowey keep on going when there was only water to mow?

When she got closer, she could see long reeds in the mower blades. Then she understood. The long reeds did not get chewed up as fast as grass. They kept the mower going, even in the water.

But the reeds were almost gone. The lawn was all cut short. Even Mowey seemed to understand this. Why else was it coming to her side of the river? There was only sand here, and a gravel road.

The children in the water looked wet and tired and worried. Celia wanted to cheer them up.

“It has to quit soon!” she called across the water. “There’s nothing left for it to mow!”

Abner lifted his damp head and shook it. He said something over the whirr of the mower.

“What did you say?” Celia cupped her hand around her ear.

This time, Tate and Derek shouted along with Abner, “LOOK BEHIND YOU!”

Celia turned around. And then she saw what she had not noticed before.

The farmer’s field of alfalfa was green and thick. It stretched as far as she could see. It looked like the biggest lawn in the world.

That was why the lawn mower was crossing the river!

Celia had to keep it from mowing the farmer’s alfalfa. But how? Her brothers and sister had not been able to stop Mowey. Her parents were away from home. And the farmer had not even seen her.

All she had was Mr. Bunny. And Mr. Bunny couldn’t do anything.

Or … could he?

Celia gasped. She had an idea! She was almost sure it would work. But she could hardly stand to think about it.

Mowey was chewing up the last few reeds on her side of the river. Soon it would roar up onto land again, and then—

Celia gulped. She bent her head and kissed Mr. Bunny under his chin, where he was softest. Then she whispered her idea in one of his long, silky ears.

Mr. Bunny did not shake his head to say no. He looked at her with steady eyes.

“All right, then,” Celia said. “You are a brave, brave rabbit.”

She crouched. She watched. And when the lawn mower crunched up on the sand, Celia and Mr. Bunny did what they had to do.

Celia looked away. She couldn’t watch. But she heard the mower choke. It gave a last rasping sigh, and then it stopped. No mower, not even a magic one, can keep on going when its blades are clogged with a stuffed rabbit.

Abner, Tate, and Derek slogged out of the river, dripping. They untangled themselves from the net. They stood in a circle around the mower, looking down.

“Wow,” said Abner.

Derek patted Celia on the back. “Good old Mr. Bunny,” he said. “He took one for the team.”

Tate gave Celia a hug. “We’ll give him a good funeral.”

“A funeral?” Derek was indignant. “Listen, when a guy on a team gets injured, they don’t bury him. They bring out the stretcher and take him to the hospital. Come on, Celia. Let’s go get the wagon.”

By the time Derek and Celia rattled the wagon over the bridge, the others had dusted every bit of green from the mower’s blades. Abner lifted the mower into the red wagon. Slowly, carefully, he pulled at Mr. Bunny’s paw. Bit by bit, the blades turned and the rabbit came free.

Abner handed what was left of Mr. Bunny to Celia. She tried very hard not to cry.

“Listen!” Derek said. “Do you hear the car?”

The dark blue sedan rolled up onto the bridge and stopped. Mr. Willow got out and stared at the freshly mown hill.

Mother got out, too, and gasped. “What on earth have you children been doing? You’re all filthy, head to toe! And dripping wet! Have you been playing mudball?”

Derek grinned. Mowing the lawn with his brother and sisters had been better than mudball. It had been more exciting than any sport he had played in his life.

His father found his voice at last. “I don’t believe it! I don’t believe you mowed the whole thing!”

The children gazed up at the beautifully shorn hill.

“We can hardly believe it, either,” said Tate.

There was a rumble from the nearby field as the tractor pulled up. A man with white hair climbed down and tugged at his cap. “Hi, folks. I saw your car, and thought I’d come meet the new neighbors. My name is Bud Wopter.”

The grown-ups shook hands. They said the sort of things grown-ups always say when they meet. They talked about the weather. They talked about their work. Mr. Wopter said he sometimes did odd jobs around town, or for neighbors.

Then the man said something interesting. He said that there had once been a mine under their house. “Yep. Hollowstone Mine, they called it.”

Abner, Tate, Derek, and Celia were suddenly alert. The last time magic had happened to them, a hamster had said that their house was built on Hollowstone Hill. Was there really an old mine underneath their house?

Mr. Wopter scratched under his cap. “You might want to get your buildings tested,” he said. “Living on top of a mine, and all. There might be radon, or something.”

“Thanks,” said Mr. Willow, “but I called ahead and had the buildings tested before we moved in. It’s all safe.”

“Might be other things besides radon,” Mr. Wopter suggested. “I could check that for you. I have a special tester I rigged up. You never know what could be seeping up through the earth from that mine. I’ve heard some stories over the years—”

Mrs. Willow interrupted and put a hand on her husband’s arm. “I’m sorry, but we need to get the children out of these muddy clothes.”

“You just call me,” said Bud Wopter, shaking Mr. Willow’s hand. “Anytime.” He nodded to Mrs. Willow, grinned at the children, and shambled off to his tractor.

“Honestly, that man!” said Mrs. Willow.

Mr. Willow chuckled. “He just wants an excuse to test his invention. I might even tell him to bring it over someday. He won’t find any radon—”

“I should hope not!” said Mrs. Willow.

“—but he might discover a whole new element. Like, say, ‘quack-ium’? Or maybe ‘goof-ium’?”

“Weird-ium!” said Tate, getting into the spirit of things.

“Doof-ium!” suggested Abner.

“Or maybe magic-ium!” Celia whispered.

Mr. and Mrs. Willow laughed.

Derek decided he had better change the subject. “Dad? Did you look at new mowers?” he asked.

“Yes,” said his father. “But we won’t have to get one until the next paycheck, thanks to you kids.” He gazed up at the hill again and shook his head in wonder. “You mowed the whole thing. I wouldn’t have thought it was even possible. You must have been going at top speed the whole time!”

“We were going pretty fast,” said Celia, remembering how dizzy she had gotten when the mower went in circles.

Mother’s eyebrows went up. “But you weren’t supposed to be mowing, young lady.”

“I wasn’t,” said Celia, and she felt this was true. She had been trying to stop the mower, which was a completely different thing. But she wasn’t sure that her mother would understand this fine point.

Abner spoke up. “She never even touched the mower,” he said. “Honest.”

Mother frowned slightly. “But she said, ‘We were going fast.’ ”

“People always say ‘we’ when they’re part of a team,” said Derek. He clapped Celia on the shoulder. “Even if they’re not on the field.”

“And she helped us a lot,” said Tate. “She made lemonade, for one thing.” She smiled at her sister.

Celia was glad Tate hadn’t mentioned the spilled sugar. She thought her mother would probably figure it out when her feet stuck to the kitchen floor, though.

“And what on earth happened to Mr. Bunny?” Mrs. Willow wanted to know.

Celia gazed down at the lumpy bundle in her hands. She was sad, but she was proud, too. Mr. Bunny had saved them from disaster.

She looked up at her mother. “He took one for the team.”