Lizzie hummed a happy tune as she dressed for school the next day. She was excited. This felt like a whole new beginning for AAA Dynamic Dog Walkers. And she could hardly wait to start handing out the new flyers.

“Make a negative into a positive,” her dad had told her once, when she had complained about being stuck on a bad volleyball team in gym class. She hadn’t really understood at the time what he meant, but now she did. Instead of being upset or worried or mad about Daphne’s trying to steal their clients, Lizzie had decided to take it as an opportunity to make her and Maria’s business better than ever.

She brought the new flyer to school that day, tucked carefully away in the back of her notebook. At recess time, she pulled Maria aside and they waited until everybody else had left the room. Lizzie even checked the cubby area in the back of their classroom, to make sure nobody — like Daphne Drake, for example — was listening. She felt like a spy with top-secret documents in her possession. “What do you think?” she whispered. She opened her notebook to show Maria the flyer.

Maria nodded. “Nice. But that’s a pretty big drop in our price, isn’t it?”

Lizzie waved a hand. “If we add a few more clients, it won’t matter if our price is lower. In the long run, we’ll make even more money. Ms. Dobbins will be so happy.” Ms. Dobbins was the director of Caring Paws, the animal shelter where Lizzie volunteered sometimes. She and Maria had pledged to donate 10 percent of their earnings to the shelter.

“More clients?” Maria stared at her. “We’re barely keeping up with the ones we already have.”

“Do you want to save our business or not?” Lizzie demanded.

For a moment, Maria didn’t answer. She looked down at her sneakers. “I guess so,” she finally mumbled.

*  *  *

After school that day, Lizzie met Maria at their usual corner. Maria had already picked up Tank and Atlas. “You’re late,” she said.

“Sorry,” said Lizzie. “I stopped to stick up a few flyers.” She held up a sheaf of papers. She had pinned a few to telephone poles and stuffed some more into mailboxes at the ends of people’s driveways. “But I’m here now.” She took Tank’s leash. “And I didn’t bring any puppies with me, notice?” She grinned at Maria.

Lizzie had set the timer feature on her watch, to make sure they gave each dog at least a twenty-minute walk. She had stuffed her favorite dog-training book into her backpack, along with the flyers, tape, and pushpins. She had looked through the book the night before and stuck Post-it notes on all the pages that had good training exercises or tips, and during their walks that day she and Maria tried out at least one with every dog. Lizzie also made sure to give each dog some special attention: an ear rub for Tank, a belly scratching for Scruffy, and hugs and extra pats for Pixie and Pogo, the twin poodles.

They handed out flyers to their customers, or stuck them in their mailboxes. “Huh,” said Ms. Federico when she read the one they gave her. “You’re lowering your price. That’s terrific! How often does that happen?”

Maria shot Lizzie a look, but Lizzie just ignored it and smiled at Ms. Federico. “Just trying to do our best to give you great service,” she said.

*  *  *

At the end of the afternoon, Lizzie volunteered to walk Ginger on her own. “I’ll take Oscar over again,” she told Maria. “I think it was really good for him to be around another dog, and Ginger seemed to enjoy the company.”

She went home and picked up Oscar, then headed off to Ginger’s house, posting flyers along the way. She put one up on a telephone pole, handed one to a teenage boy who was walking a beagle, then stuffed a couple into mailboxes. She was two doors away from Ginger’s house, putting a flyer into another mailbox, when she spotted a mailman across the street. She smiled and waved, wondering if he carried dog biscuits in his bag, the way Rita, their mail deliverer, did. Rita was so friendly, and she loved dogs. She would always stop to ask about whatever new foster puppy Lizzie was walking, and give it pets and treats. Rita hadn’t met Oscar yet, but Lizzie knew she would love him when she did.

But instead of smiling and waving back, the mailman trotted across the street toward Lizzie, frowning. “You’re not allowed to do that, you know,” he said, waving a hand at the flyer she was stuffing into a red mailbox. “Only employees of the United States Postal Service can put mail into mailboxes.”

“It’s just a flyer,” Lizzie said, holding it out to show him, “for my dog-walking business.”

He didn’t even glance at it. “You’re breaking the law,” he said. “Regulation 3.1.3 states clearly that anyone putting anything other than US mail into a mailbox can be prosecuted and fined.”

“Oh.” Lizzie let her arm drop. This mailman wasn’t anything like Rita. In fact, the way he’d charged over and growled at her reminded her of the way Oscar had behaved when he spotted Bowser that day at Aunt Amanda’s. “Sorry. I won’t do it anymore,” she said, looking down at the ground.

“I imagine you won’t, now that you know it’s against the law,” said the mailman, and now his voice was a little gentler. He reached into his mailbag. “Would your pup like a biscuit?”

Lizzie looked down at Oscar. He thumped his tail on the sidewalk.

I believe I heard the word “biscuit” mentioned. Does that mean —

“Sure,” said Lizzie. She didn’t bother explaining that Oscar wasn’t exactly her pup. The mailman bent down and gave Oscar a bone-shaped dog biscuit.

“Good boy,” he murmured. “Aren’t you a good-looking gentleman?”

Lizzie smiled to herself. Everybody loved dogs. Maybe this mailman wasn’t such a meanie after all. Maybe he only acted grouchy sometimes, just like Oscar. “His name is Oscar,” she said.

“Well, Oscar,” said the mailman. “How about one more biscuit?”

Oscar’s tail thumped again. He put up a paw.

“Oh, you shake hands, too? What a smartie.” The mailman dug out another biscuit and handed it over.

Lizzie was still smiling as she walked up to Ginger’s house. She told Oscar to sit and knocked on the door.

Anjali was not smiling when she opened the door. In fact, she looked as if she’d been crying. “Oh, Lizzie,” she said. “I almost forgot you were coming. I’m so glad you’re here. Ginger is not doing well today. She’s not doing well at all.”