The Triangle Secret - The Math Kids (Book 6)

When FBI Special Agent Carlson is kidnapped while investigating the plane crash of Willard Howell, an eccentric billionaire inventor, the Math Kids spring into action. If Catherine, Stephanie, Justin, and Jordan can figure out the Great Triangle mentioned in Howell's will, they might just uncover who's behind the crash and Agent Carlson's kidnapping—if they don't get caught themselves! The Math Kids: The Triangle Secret is the sixth book in the Math Kids series.