I, Huckleberry by Simon Chesterman

Magna Carta: The most famous legal text in history. The foundation of the rule of law. Stolen. When Huckleberry Jones is packed off by his parents from New York to a camp for “exceptional teenagers” at Oxford University, his first question is: Why? But meeting the beautiful, enigmatic Kat might just make his time there worthwhile. Together with new friends Mei and Tshombe, he discovers that teenagers from four continents can have more in common than their differences. Then Huck finds himself trapped in a mystery linked to an 800-year-old parchment—and solving it could cost him his life.