An American falls for the princess of the Kingdom of Graustark, and decides to her marriage to a dastardly prince.

While traveling by train from Denver to Washington, DC, wealthy young Grenfall Lorry meets a beautiful young girl. When they are accidentally left behind in a mining town, they race through the mountains and finally catch it. They travel to Washington and have a great time, but they soon part. They meet again later in the small European country of Graustark, where Grenfall and his friend Harry rescue her from kidnappers, and they then discover that she is actually the country's Princess Yetiva. She is engaged to Prinze Lorenz of Asphan in order to pay off Graustark's enormous debt from the war, but Lorenz is murdered and Grenfall is framed for the crime. Complications ensue.

Beverly Calhoun is invited by her friend, Princess Yestive of Graustark, to pay her a visit. On her journey, she is waylaid by bandits, and becomes entangled in the political problems of a neighboring country, whose ruler Prince Dantan, has been ousted by his evil half-brother Gabriel. Dantan, disguised as a simple goat hunter, has been driven into hiding in the mountains with his followers. Beverly is rescued by his band of rebels, but is mistaken for Princess Yestive. Beverly and Dantan fall in love, but their romance is complicated, not only by the hostilities between the two countries, but also because neither of them knows the true identity of the other.

Graustark needs thirty million dollars to satisfy a Russian loan. The Prince of Dawsbergen, ruler of the adjoining principality, will advance the money if the young Prince of Graustark marries his daughter. Prince Robin, however, inherits an independent spirit, his father having been an American. He refuses absolutely to marry a Princess whom he has never seen. His councilors plead in vain. With the ruin of his country imminent, the boy ruler hastily sails for America to negotiate the loan, hoping at the same time to meet the girl of his dreams. The money is readily advanced by William W. Blithers, a self-made millionaire anxious to have his daughter marry into royalty. The daughter, however, avoids the Prince and he does not see her. He rescues a girl from drowning and falls in love with her. He believes her to be Blithers' daughter, but she does not reveal her identity.