Ben, Zara, Sam and Marcia begin their summer vacation by helping Professor Ampersand build the Silver Turtle, a high-tech airplane. This is thrilling enough, but things take an even wilder turn when a strange woman steals the airplane with the kids inside. She's trying to evade members of Noctarma, an international criminal organization that thinks the airplane is carrying a secret antigravity device that could be the key to world domination. They've got the wrong Silver Turtle, but they've also captured Professor Ampersand—and the kids will have to pull out all the stops to find the real Silver Turtle device before Noctarma does.