Truxton King.

An American seeking adventure in Graustark strikes up an acquaintance with six-year-old Prince Robin and his Aunt Lorraine. The next day, Truxton overhears a plot against the prince and is taken prisoner. He escapes to rescue both Prince Robin and Lorraine, and to prevent an attack on the castle. Truxton's love for Lorraine leads to marriage when she reveals that she, too, is American.