Bestselling adult author Cussler meshes fantasy and adventure in this lighthearted tale, which opens on a California farm. After an itinerant farmhand arrives to help the Nicefolk family with the harvest, twin 10-year-old siblings Casey and Lacey begin to hear "unexplainable tinkling and clinking noises" coming from the barn. On his departure, the stranger gives the kids a contraption that can make toys life-size - but they must only use the device to do good and must keep it a secret.

Cussler sets his tale at a time when steamboats still traveled the Mississippi: Casey builds a replica of the Wright brothers' biplane, Flyer, which he names Vin Fiz (after his favorite soda pop), and uses the magical machine to enlarge it. The twins and their dog take off on a cross-country flight in the aircraft, which possesses a "mystical vision" that draws it to people in danger. Under her guidance, the youngsters help free Nevada townsfolk forced by scoundrels to labor in a gold mine, halt a runaway train overtaken by bandits in Ohio and stop two girls from tumbling over Niagara Falls.

Cussler sprinkles his folksy narrative with instructional notes ("A line, by the way, is nautical talk for rope") and facts (almost 800,000 gallons of water rush over Niagara Falls every second), and characters' names emphasize the text's tall-tale quality (e.g., Ever and Ima Nicefolk, Stoke and Blaze Firepit). This genial, at times suspenseful, caper wraps up with a note about the real Vin Fiz.