After his uncle's death, Harry Gilder takes ownership of a ketch, the Bridget B., which he renames the Ina. The ketch is chartered by a man named Jamieson and his colleague Albot, for a trip to Tofumira, 300 miles north of Fiji. Harry invites his friend, Norman, along, intending to 'combine business with pleasure'.
On the journey, Harry discovers onboard a letter from his uncle that outlines a legacy of valuable pearls hidden on the island, of which Jamieson and Albot are aware. A battle ensues for the recovery of the pearls and a safe return to Melbourne.
Fourteen year old Billy Marsden attends boarding school in Christchurch and misses her friend, Judy. On the last day of term, she overhears one of the station hands organising a burglary of her family's property in the country. Billy races home, collects Judy, and heads off to stop the criminals.