After days of dead calm on the Pacific Ocean, a couple sailing around the world take refuge in the lagoon of an uncharted island and attempt to repair the engine of their sailboat. Although they believe the tiny atoll to be uninhabited, it is actually home to a mysterious woman who has been stranded on the remote strip of land for more than forty years.

As the castaway's absorbing tale unfolds, the reader discovers her possible identity and learns how she loved and lost, suffered hardship and loneliness and eventually surrendered to the island's tropical beauty. Interwoven with this dramatic narrative is the story of Robin and Lucy's struggle to repair their boat and restore meaning to their long journey. Thus far, their dream of tranquillity and romance on the seas has brought only discord to their marriage.

They are at odds with each other, beleaguered by their misfortunes and by a long-standing argument about whether to have a child. As Robin and Lucy become more estranged, the castaway observes them and leaves puzzling hints of her presence, unsure if she should reveal her existence and risk returning to society. Before she can reach a decision, an encroaching storm threatens to change the course of all their lives.