“I have something,” Simon said. The group gathered around him.

Simon tapped to the name of a researcher on one of the posters. “Professor Apple. Get it?”

“Get what?” Cooper said. “What does Professor Apple have to do with finding Dr. Newton?”

“Simple,” Chelsea said. “The story is that Newton discovered gravity after getting bonked on the head with an apple.”

“I think the real story,” Jamal said, “is he saw an apple fall from a tree.”

“That’s got to be the clue,” Simon said. “Maybe Dr. Newton is in Professor Apple’s lab.”

Gabby checked the building directory. “Her lab is on the second floor.”

“Let’s go,” Chelsea said.

The group dashed toward the stairway.

“No running, Trackers,” Mr. C said as he and Pascal tried to catch up.

The kids switched to a fast walk.

“We’re about to find Dr. Newton!” Simon pumped his fist in the air.

The door to Professor Apple’s lab was open, and the Trackers hustled in before Mr. C had a chance to knock.