The marble slowed as it rolled past a long platform. Samantha could see a doorway at the far end of the platform with stairs leading up and out of sight.

It reminded her of the subway stations in New York City.

“Let’s stop here and look around,” she said.

She reached for the handle in their marble’s round door and gave it a quick twist. The ball came to a stop, and she pushed the door outward.

“Uitgang means exit,” said Fiona, pointing at the sign on the wall.

UITGANG:

ALLEN

PARK

“Allen Park, Michigan,” said Lainey. “That’s where you can find the world’s biggest tire.”

“Why would you even know that?” asked Fiona.

“If you want to be an expert on brothers, you have to learn a whole lot of useless facts,” Lainey answered.

Samantha thought about telling Lainey to join WRUF, the Worldwide Reciters of Useless Facts. She changed her mind.

“Do you think there’s any chance Nipper got off the ride here?” asked Samantha.

“Possibly,” said Fiona. “Your brother sounds like one of those boys who get hungry a lot.”

“No,” said Lainey. “He kept rolling.”

“How do you know that?” Fiona asked.

Lainey opened her hand, revealing a dozen miniature gears, screws, and other tiny items.

“I’ve been collecting little bits of machinery from the ground,” she explained. “I found some of it along the way to the kogelbaan. I don’t see anything similar here. So I don’t think Samantha’s brother got out of his ball at this station.”

Samantha and Fiona looked at the shiny items in Lainey’s palm.

“Okay,” said Fiona. “But how do you even know they’re from Sam’s brother?”

Lainey turned to Samantha.

“Did your brother ever carry a pocket watch?” she asked.

“Maybe,” she answered. “Are you thinking it’s a really fancy pocket watch?”

“Very likely,” Lainey answered. “Most of these pieces seem to be gold, and there are some tiny jewels, too. They might be sapphires.”

Samantha could see that some of the tiny bits sparkled.

“And…does it look like somebody let it drop and break into thousands of pieces?” Samantha asked.

“It seems that way,” said Lainey.

“Then yes,” said Samantha. “My brother carried that pocket watch.”

“All right, then,” said Lainey, heading back to the track. “Let’s go look for boys!”

Samantha and Fiona didn’t move.

“I mean look for a boy,” Lainey said, “singular.”

Samantha shook her head, but she smiled a little, too. It was kind of funny.

“Wait,” said Fiona, suddenly sounding worried. “Come here.”

She stood by the exit sign, pointing to something. Samantha and Fiona walked over and joined her.

They saw a map of the U.S. painted on the wall to one side of the exit. One long, meandering dotted line connected seven circles. The number twelve appeared in each corner of the map.

“These are the seven stations of track twelve,” said Fiona. “We’re in Michigan, right here.”

Samantha spotted the state of Michigan easily. Anyone could. It looks like a mitten.

“There are six more stops before we get back to Seattle,” Fiona noted.

“Got it,” said Lainey. “What’s the problem?”

Fiona began to trace the line with her finger.

“So far, we’ve been traveling mostly in a straight line,” she explained. “There have been a lot of curves and loops, but it’s been a direct path, more or less.”

She moved her finger along the line until she got to the fourth circle.

“That all ends here,” said Fiona. “St. Louis.”

Samantha watched Fiona’s finger as she traced the dotted line. The path twisted and turned, winding back and forth across the U.S. before it finally reached another circle.

“There are three more stops in the next few hours,” Fiona calculated. “After that, there’s a whole week before there’s another chance to get out of a ball.”

“A week?” asked Samantha.

That was a long time for super-secret travel. The magtrain and slidewalk never took longer than an hour or two at the most. Samantha made a mental note to ask her uncle about this, too, when she got home…and had a chance to learn about everything.

“I promised my parents I’d be home by dinner,” said Lainey. “I’m in trouble.”

“I know, I know,” said Fiona. “With my schedule, I can’t stay away from Seattle for a week, either.”

“Sam?” asked Lainey. “What about your little brother?”

“If he stopped at a station, do you think he paid attention and noticed the map?” asked Fiona.

“Unlikely,” Samantha and Lainey both said at the same time.

“Do you think he can stay in the ball for days and days without getting bored?” asked Lainey.

“He can’t,” said Samantha and Lainey at the same time.

Samantha tried to picture her brother in one of those locations by himself. He might be able to get home. Or…he might annoy someone and get chopped into cubes. Or attacked by a clown or a dangerous animal or a pirate. Or he might get flushed into a bottomless pit.

“Okay, Lainey,” said Samantha. “Based on everything you know, what’s the absolute farthest station a boy would ride to before he got bored, started fidgeting, and got out?”

Lainey joined her in front of the map. She traced the dotted line with her finger.

“Fun…fun…,” she said as she traced. “Fun…not-so-fun…boring.”

Her finger stopped at a circle between Illinois and Missouri.

“Too bad there’s no shortcut between these stations,” Fiona mused out loud. “Whoever built this system really didn’t think about—”

“Wait,” Samantha interrupted. “Why is that too bad?”

Fiona pointed to their location on the map again.

“If we could just skip from here to Mitchell or Cawker City, then we could roll home in a few hours instead of seven days,” she said.

“Seven Days!” wailed Lainey.

While Fiona and Lainey stared at the map, Samantha walked to the edge of the platform. She wanted to be as far away from the other girls as she could without drawing attention to herself.

“I’m going to be in so much trouble,” she heard Lainey moan.

“I think we’ll start dying of thirst…about…here,” she heard Fiona explain in a matter-of-fact voice.

Samantha opened her umbrella and put it on the floor. She pulled out Nipper’s hand lens. This was an emergency. She had to work quickly. She studied the lining until she found what she needed and quickly snapped the umbrella shut.

“Okay, girls,” she called. “I know a shortcut.”

She pointed at them with her umbrella.

“But it’s super-secret.”