Twelve-year-old Sam adores her grandmother, but Grandma will be at work most of the time during Sam's visit, leaving Sam with the Colonel, her prickly grandfather. Sam's relationship with him is shaky at best, and now that the Colonel has had to retire from his career as a military pilot, he is harder than ever to get along with. Sam reluctantly settles in for the summer, entertaining herself with her nonstop collection of off-beat trivia and her obsession with the Guinness Book of World Records. Sam soon finds that her grandfather's behavior is even stranger than she expected. He disappears for long stretches of time and won't let Sam go into the old barn. She is eager to solve the mystery, but when she discovers that the Colonel is building an airplane against his wife's orders, she makes a deal with him. If he lets her help him finish the plane, she'll keep his secret. As the pair work together, they find out how much they have in common, and persistent Sam finds a way to help her grandfather achieve a lifetime dream.