The Castaways follow sisters Lori and Erin as they embark on the holiday of a lifetime in Fiji. However, after a huge fight Erin never boards the island-hopping flight to their resort – and the plane, with Lori on board, never arrives at its destination.

Months later, with no wreckage or survivors having been found, Lori's credit card is suddenly used in a corner shop in a remote village in Fiji, and on CCTV Erin recognises the plane's pilot. She sets out on a journey to find him and discover the mystery of what happened to her sister.