Samantha followed her uncle through Central Park and walked up the same staircase she had climbed with Nipper over a month ago. In the center of a redbrick terrace, a huge stone obelisk emerged from a square granite base.

“Cleopatra’s Needle,” said Samantha. “I was here with Nipper last month.”

Uncle Paul nodded. He hopped over the metal railing that surrounded the monument.

“Climb over, and let’s get this thing moving,” he said.

She gazed up at the towering stone monument. Worn carvings of ancient Egyptian symbols covered every surface. She shrugged and placed her trombone case on the other side of the railing. Then she took her uncle’s hand. He helped her scale the three-foot-high barrier and hop down. As soon as she landed, he let go and stepped up to the obelisk. He leaned into it, shoving hard with both hands.

“Push with me,” said Uncle Paul.

Together they strained and shoved until, suddenly, it budged.

A deep scraping sound rumbled, and the giant obelisk began to turn. At first, it felt very heavy and was difficult to move. After a quarter rotation, it seemed to loosen a bit. It still took some strength, but the obelisk began to move more easily.

“I can’t believe it,” said Samantha.

“Believe what?” Uncle Paul asked. “That there’s a secret entrance? This can’t be the most amazing thing you’ve seen so far.”

“No,” Samantha replied. “I can’t believe Nipper was right about moving this monument.”

The obelisk rotated as they continued to push a second time around the granite base.

“This is so much harder alone,” her uncle said as they pushed. “Here comes three.”

Just as they reached the end of the third cycle, two metallic clicks echoed inside the stone base. It sounded like a large, heavy lock opening.

Uncle Paul stopped pushing, so Samantha did, too. He grabbed her suitcase, knelt down, and pushed on the side of the monument base. It swung inward, like a dog door. He looked back at her.

“See you at the bottom,” he said.

Then he winked and disappeared through the swinging door.

Samantha looked around the terrace to make sure she was alone. She slipped her arm through the large handle of her trombone case, turned back to the panel, and pushed her head inside. A dimly lit shaft led straight down below the needle. A ladder on the far wall lined the shaft. Looking down, she could just barely make out the shape of her uncle, working his way down the ladder.

She reached out and grasped a ladder rung with her free hand, stepped out with one foot, and let her trombone case hang from her arm.

Slowly and somewhat awkwardly, she started to climb down.

“I made it,” her uncle called from somewhere beneath her. “Sixty-nine feet under the park.”

Samantha remembered that Cleopatra’s Needle rose sixty-nine feet above the ground. She didn’t get many chances to look down as she descended, however. During most of the climb, she kept her eyes on her hands—and her hands on the ladder. It would be good to get home so she could ditch the trombone case. Traveling with the umbrella was easy—when you could just sling it over your shoulder.

After a while, the space around her grew brighter. Samantha stopped to check out her surroundings. The shaft had widened as she’d climbed down. Below her was an empty chamber with one open exit. She only had a few feet to go, so she climbed down three more rungs and then hopped onto the floor, landing hard on cement. The trombone case slid down her arm, but she grabbed the handle before she dropped it. It took a few seconds to regain her balance.

Uncle Paul wasn’t there.

“Hello?” she said.

Her voice echoed back up the shaft.

“Over here,” Uncle Paul called. “I’m at the slingshot trolley.”

Samantha followed her uncle’s voice through the exit and into a hallway where he was standing in another chamber beside a shiny silver vehicle. She guessed it was about twice as long as a car. It came to a long point in the front. A clear canopy rested on a hinge at an angle, revealing a two-person cockpit. Fins stuck out the back. To Samantha, it looked like a fighter jet without wings.

“So that’s the slingshot trolley,” she said.

“Yes. That’s what they call it,” said her uncle. “I know you’re much better at making up names for things like this.”

“Actually, yes,” said Samantha. “On the way to Machu Picchu, I made up dozens of names for the terrace train, or the balcony buggy, or— Wait. Who’s they?”

She hoped to get some actual information now, but Uncle Paul had already climbed up and over the side of the strange vehicle. He sat inside the cockpit with her suitcase on his lap and waved for her to join him.

Samantha grabbed the edge of the opening with both hands and pulled herself over the side. She landed on a padded leather bench next to her uncle.

His hand hovered over a bright red button on the dashboard in front of them.

“Buckle up,” he told her. “You’ll like this.”

Samantha looked down and saw two parts of an X-shaped harness. It was just like the restraint on the terrible rocket ride from Mali to Indonesia—when Nipper launched the hydro rocket before she had a chance to “buckle up.” She put the trombone case on the floor between her feet and snapped the two parts of the harness together quickly.

“Hang on,” said Uncle Paul. “I’ve done this a hundred times, and it’s still always a bit of a jolt.”

He slapped the button.

Hiss. Hiss. Hiss. Hiss.

The vehicle slid backward a few feet and then again three more times.

Uncle Paul slapped the button again.

A hurricane of steam swirled around the vehicle and…

SHOOM!

Samantha sank back into her chair as they shot forward. The walls of the tunnel blurred, and she felt pressure on her eyelids. It was hard to blink. She could barely move. The force of the acceleration kept her pressed tight against the back of the seat. Her arms stayed stuck at her sides. But she was fine with that. Happily, unlike that time on the hydro rocket, she felt prepared for this ride. Also, she wasn’t upside down, shoeless, and sopping wet.

“I bet this is what it’s like to take off from an aircraft carrier,” Uncle Paul said over the sound of the vibrating, speeding craft.

Samantha eyed one of the metal fasteners holding the cockpit together. It reminded her of the rivets on the Eiffel Tower. Did the same people design these things? She really needed to find some way to get her uncle to tell her everything.

“So, who built this…trolley?” she asked casually.

“Same folks who built the magtrain,” Uncle Paul answered.

“And who were they?” she asked.

“Well,” said Uncle Paul, “the same folks who—”

“And who were they?” Samantha interrupted, a little louder.

“Ah yes,” said Uncle Paul, gazing around the cockpit.

He looked right at her with a serious expression.

“We’ve got almost an hour until we reach Dynamite,” he said. “Let’s start…almost at the beginning this time.”

Samantha tried not to show her excitement. She waited, hoping that this was finally it, the moment when she would learn everything.

“There’s a magtrain station at Dynamite, Washington,” he said.

“Oh, I know that,” said Samantha. “I want to know who built it.”

Uncle Paul smiled and nodded.

“Yes, I’ll start by giving you a WEATHER report,” he said.

Samantha smiled. “And the slidewalks,” she said. “I want to know all the places they go.”

“Of course,” said Uncle Paul.

“And what’s up with dog clogs?” she added.

Uncle Paul stopped smiling.

Samantha immediately regretted her words. Her uncle was staring off into space again. He began to rub his forehead. She had no idea what he was thinking.

Lights pulsed overhead as they rocketed through the tunnel. Samantha glanced around the cab and noticed a small compartment behind them. Several shiny rectangular objects rested on the floor.

“Are those gold bars?” she asked.

“Maybe,” said Uncle Paul. “Wait. I’m sorry. What did you say?”

Samantha didn’t ask again.

She had lost him to the dog clogs for the second time that day. Would he recover before they reached home?

The slingshot trolley hurtled onward.

Samantha thought about Nipper, somewhere in Seattle. She would help her dad find her brother. Then maybe she’d spend a little time on her own life—the not-so-super-secret parts that included summer and friends.

Okay, maybe not so many friends, she told herself. In the past few months, she’d spent so much time racing around the world with her brother, defeating the RAIN and the SUN, she hadn’t had much time for friends. She didn’t even have many sort-of, kind-of friends out there.

“Dog clogs,” Uncle Paul said again.

Samantha decided that as soon as she saved Nipper, she’d definitely make some new friends.

Sort of, kind of.