The story is written as a first person narrative from the perspective of 15-year-old Ralph Rover, one of three boys shipwrecked on the coral reef of a large but uninhabited Polynesian island. The account starts briskly; only four pages are devoted to Ralph's early life and a further fourteen to his voyage to the Pacific Ocean on board the Arrow. He and his two companions – 18-year-old Jack Martin and 13-year-old Peterkin Gay – are the sole survivors of the shipwreck. The narrative is in two parts. The first describes how the boys feed themselves, what they drink, the clothing and shelter they fashion, and how they cope with having to rely on their own resources. The second half of the novel is more action-packed, featuring conflicts with pirates, fighting between the native Polynesians, and the conversion efforts of Christian missionaries.