When Wade Kaplan receives a mysterious package containing an ancient astronomical artifact after his astrophysicist uncle dies suspiciously, he and three friends—Lily, Darrell, and Becca—are plunged into a dangerous international adventure. They discover their uncle was part of a secret society called the Guardians, protecting a powerful relic called the Copernicus Legacy: a celestial machine that could unlock immense power. Racing against a ruthless secret organization called the Teutonic Order, the four kids must follow clues across Europe, solve historical puzzles, and protect the legacy from falling into the wrong hands.