Helen and Ridley Ambrose are preparing to set off for an exotic resort off the coast of South America on the Euphrosyne, a ship belonging to Helen's brother-in-law Willoughby Vinrace. Travelling with them is his daughter Rachel - a quiet, unremarkable girl raised in the London suburbs by her spinster aunts after the death of her mother. Along the way other people come aboard, such as the upper-class Clarissa and Richard Dalloway. As Rachel interacts with the passengers, intrigued by their different personalities, it becomes clear that what started for her as a mere sea voyage is turning into a journey of self-discovery and a rite of passage that will change her for ever.