Fifteen year-old Rollin's father was abandoned by his crew on the North Kimberley coast, near the Darke River off Cape Leveque. When the Swallow returns to the region under Captain Chadwick, Rollin and Ben leave the ship to search for Rollin's father and the mysterious city of Oo. They are pursued by Chadwick's crew, set upon by 'native savages' and eventually gain the support of an Aboriginal man, Polly, who helps them along their journey.
After a long journey, they reach Orbello, a village protected by short, dark-skinned soldiers, wearing helmets common to the Middle Ages. Rollin's father, a stranger in a strange land, had been made King of Orbello. Rollin finds his father, defends the Orbello against the Lundee warriors, and locates the city of Oo, where he is rewarded with diamonds.
