"Really? You have a mystery for us to solve?" Maggie asked Nathan eagerly.
Henry stared at the five-dollar bill that Nathan had just slapped down on the lemonade stand.
He felt a flutter of excitement.
"Cool!" he said.
"What's the mystery?" Cole sounded excited too.
"It's about my little sister Nora," Nathan told them.
"She's been acting weird lately."
Henry's excited feeling faded. He traded a look with Maggie and Cole.
Cole looked disappointed. Maggie rolled her eyes.
"What's the mystery about that?" Maggie asked Nathan.
"No offense, but Nora always acts kind of weird."
"Yeah." Cole laughed. "Remember when she wore those pink pants every day for a week, and wanted everyone to call her Princess Pretty Pants?"
"That's nothing," Maggie said.
"What about the time she pretended she was an alien from outer space?"
Henry nodded. Nora was only five years old, but she was famous in the neighborhood for doing strange stuff.
"She argues with everybody about everything," Henry added.
"And she's always dragging her stuffed animals around and pretending they're real."
Nathan grinned.
"She pretends her stuffed animals are real because she wants a pet so badly.
She begged for a puppy for her fourth birthday, but Mom and Dad said no pets."
"So it's no mystery that she's acting weird," Cole told Nathan again.
Nathan shook his head. "This is different," he said.
"Mom and Dad are really worried. They think Nora has been sleepwalking!
They've caught her a couple of times walking around outside after dark."
"Nora's been sleepwalking?" Henry said.
"That sounds kind of serious, but it's not really a mystery."
"I said they think she's been sleepwalking," Nathan said.
"I think she's faking!"
"Why do you think that?" Henry asked.
"It's just a feeling," Nathan said.
"I think she's up to something sneaky, but I'm not sure what it is."
Maggie shrugged. "So what? Why do you care if she's pretending to sleepwalk?"
"I just want to find out the truth," Nathan said.
"Like I said, my parents are really worried about her.
They're planning to take her to the doctor next week.
If she's really sleepwalking, that's okay.
But if she's faking it, she's making them worry for nothing! That's not fair."
Henry still wasn't sure that this counted as a mystery.
But Nathan was their friend, and he seemed pretty worried.
Besides, investigating a mystery was better than sitting around pouring lemonade all day.
"We can look into it, I guess," Henry said.
Cole picked up the five-dollar bill.
"But you should take this back for now," he told Nathan.
"What are you doing, Cole?" Maggie cried.
"This may not be much of a mystery, but that doesn't mean we'll solve it for free!"
"I know." Cole gave the bill back to Nathan.
"But The Lemonade Detectives have a guarantee, remember?"
He pointed to the line on their sign that read "All Mysteries Solved, Guaranteed."
Maggie looked at it. "So what?" she said.
"A guarantee means Nathan only pays us when he's satisfied with our work," Cole replied.
"That's what my dad always tells his customers, and he's a businessman."
"Well, we're not businessmen," Maggie said with a frown.
"We're just kids. And I need that money for my riding lessons!"
"We'll get the money as soon as we solve the case," Cole said.
"Cole has a point, Maggie," Henry said.
"It doesn't make sense for Nathan to pay us now.
If we can't solve the case, we'll just have to give the money back."
Maggie still looked unhappy. But she nodded. "Fine," she said.
"I guess it doesn't matter as long as we solve this case fast."
Nathan tucked the five-dollar bill back into his pocket.
"So does this mean you'll try to solve my mystery?" he asked.
"Yes," Henry said. "The Lemonade Detectives are on the case!"
"Let's go to your house and talk to Nora," Cole said.
There were no customers waiting for lemonade just then.
Maggie took out a small sign that said "Back in a While" and set it on the table.
Then they all walked over to Nathan and Nora's house.
"Do you know where Nora is right now?" Maggie asked Nathan.
"She's probably in the playroom," Nathan said.
"It's at the back of the house so we can go in the back door."
He led the way around the side of the house.
They turned the corner just in time to see a window slide open.
A second later Nora climbed out and tiptoed across the backyard!