Ms. Lovelace’s office was located in a small brick building in downtown Sandford. A little sign out front read: Stella Lovelace, Attorney at Law. Marly, Isla, and Sai walked inside, and a lady behind the counter lifted her head.

Marly cleared her throat. “We’re here to see Ms. Lovelace,” she said politely.

“I’m sorry. Ms. Lovelace isn’t available right now,” the lady said, avoiding Marly’s eye. Marly was used to that. Grown-ups never liked to make eye contact with kids who wore eye patches.

“That’s okay. We’ll wait.” Sai drummed his hands on the counter.

“There are some chairs over here.” Isla pointed.

The lady stood up. “You can’t wait,” she said. “Ms. Lovelace is going to be tied up all afternoon. But if you’d like to make an appointment—” Before she got the whole sentence out, a door opened behind her.

“What’s going on?” Ms. Lovelace poked her head out. “Oh.” Her face softened when she noticed Marly, Isla, and Sai.

“We brought you something,” Sai said. “Show her, Marly.”

Marly opened their notebook, turned to the latest puzzle, and held it up. “This says you have an envelope for us.”

Ms. Lovelace smiled. “I sure do,” she said. “Be right back.” She closed her office door. Less than a minute later, she returned with a plain white envelope and a flashlight. “Here you go!” She handed them to Isla.

“Thanks,” Isla said, staring curiously at the flashlight.

“What’s the flashlight for?” Sai asked.

Ms. Lovelace offered a tight-lipped smile and went back inside her office.

“Guess that’s up to us to figure out,” Marly said. “Come on, let’s go.”

But they couldn’t wait until they got back to the tree house to find out what was inside the envelope. They hurried over to an open bench at the end of the street.

Isla set the flashlight between her and Sai, and tore open the envelope. Sai immediately grabbed the flashlight and started turning it on and off, on and off, on and off.

“Don’t,” Marly said, laying her hand over Sai’s. “It looks like you’re flashing SOS. People are going to think you need help!”

“Nuh-uh,” Sai argued. “SOS is like this.” He blinked short-short-short, long-long-long, short-short-short. “I’m doing this.” He blinked on, off, on, off. “It’s different.”

Marly rolled her eyes.

“Do you want to hear our new letter?” Isla asked, holding up another paper From the Desk of Harry P. Summerling.

“Yes! Duh!” Marly and Sai spoke at the same time.

Isla smoothed the paper on her lap and began reading. “‘Dear Treasure Troop. If you’re reading this letter, that means you have found the tree house—’”

“Because we rock!” Sai interrupted.

“‘You’ve also found the hidden cubbyhole inside the tree house,’” Isla continued. “‘And you even found a way to read my invisible ink. Clearly, I have not underestimated you three at all.’”

“No, you have not,” Sai said proudly.

Marly elbowed him. “Let her finish.”

“‘Guess what?’” Isla read. “‘There is more treasure to be found!’” They all glanced at one another, their eyes shining with anticipation. “‘You’ll find what you need inside my house, in a hidden room that looks out over the city. But finding that room won’t be easy. One ghost guards the doors. Another keeps the key. The very important key. I hope you’re not afraid of ghosts.’” Isla swallowed hard, then kept reading. “‘You have until August 25 to find the hidden room. Otherwise this treasure will be lost forever. If you ever find yourselves stuck, remember who you are. That will always get you through. Good luck! Yours, Harry P. Summerling.’”

“I can’t believe it,” Marly said. “There really is more treasure.”

“And we get to go search a haunted house to find it,” Sai said, rubbing his hands together.

A flash of concern crossed Isla’s face when Sai said haunted. But she blinked it away. “I wonder what the treasure is,” she said.

“I bet this time it’ll be money,” Sai said. They had all thought the treasure was going to be money last time. Marly had planned to use her share to buy a plane ticket to visit her friend Aubrey, who had moved away at the beginning of the summer. But she wasn’t disappointed when it wasn’t money. She still missed Aubrey, but she wasn’t as lonely as she had been at the beginning of the summer. Not since she, Isla, and Sai had started spending time together.

Sai hopped down from the bench. “So, what’s our next puzzle?” he asked eagerly.

“There isn’t one,” Isla said.

“What do you mean there isn’t one?” Marly asked. There was always another puzzle.

Isla studied the paper. “We have to find a hidden room. That’s all it says.”

“Yeah, but we’ll find it by solving a bunch of puzzles, right?” Sai said. “Like how we found the tree house.”

“I don’t know.” Isla turned the paper over. It was blank on the other side. “I don’t see any other puzzles.”

“Maybe Ms. Lovelace was supposed to give us another envelope, too,” Sai suggested.

That was how it had worked the first time. Ms. Lovelace had read that first letter from Mr. Summerling out loud. Then she gave them another envelope, which held their first puzzle.

“Let’s go ask her!” Marly said, getting up from the bench.

Isla handed the letter to Marly, who shoved it inside her bag with the notebook. Then they marched back to Ms. Lovelace’s office.

They opened the door and found Ms. Lovelace standing at the front counter, riffling through some papers inside an open folder in front of her. She quickly closed it. “Yes?” she asked with an awkward smile as Marly, Isla, and Sai approached the counter.

They all nudged one another, trying to figure out who should do the talking. Marly decided she would. “Did you maybe forget to give us another envelope?” she asked boldly. “One that has another puzzle in it?”

“No,” Ms. Lovelace said, running a hand through her hair. “I’ve given you everything I was supposed to give you.”

“Are you sure?” Sai asked.

“Positive,” Ms. Lovelace said.

Marly, Isla, and Sai exchanged surprised looks. Now what?

“Okay, thanks,” Marly said. There was nothing else to do but leave.

“So . . . ,” Isla said as they started down the street. “We’re just supposed to go over to Mr. Summerling’s house and look for a hidden room?”

“I guess?” Marly said. Though it seemed odd to her that they would have free rein to run around inside someone else’s house all by themselves. Would their parents even allow that?

“If that’s what the letter says, then that’s what we have to do,” Sai said, picking up the pace.

Marly agreed. Odd or not, they had to find the hidden room inside Mr. Summerling’s house. They had to find the new treasure.

“Wait.” Isla stopped walking. “How are we going to get inside the house?”

Marly stopped, too. “Good question,” she said, scratching her head. They had a key to the gate to Mr. Summerling’s front walk. They’d found it during the other treasure hunt. But they didn’t have a key to his house. How would they get in?

“We’ll figure it out when we get there,” Sai said impatiently. “Come on!”

Marly and Isla raised eyebrows at each other. Finally, Marly shrugged. Maybe they would figure it out when they got there.

“Okay, but let’s stop at Marly’s house and tell our parents where we’re going first,” Isla said.

“Fine,” Sai said.

They started walking again. But after a few steps, Marly suddenly had the strangest feeling someone was watching them. She turned and saw a mom pushing a little kid in a stroller, and two men in business suits carrying cups of coffee. None of them seemed to be paying any attention to the three of them.

They kept going. But still, Marly couldn’t shake that feeling. Nor could she stop glancing over her shoulder.

“What’s the matter, Marly?” Isla asked the third time she did it. “Why do you keep turning around?”

“I don’t know,” Marly said. “I just have this weird feeling that someone’s watching us.”

“Who?” Isla asked.

“I don’t know,” Marly said again.

Sai turned all the way around. “I don’t see anyone.”

“Neither do I,” Isla said.

Marly knew Isla and Sai both had way better eyes than she did. If they didn’t see anyone, then there probably wasn’t anyone there.

“Let’s just go,” she said.