Following the death of their father, sisters Eva and Carolina Villanueva travel on the ocean liner, Bárbara de Braganza (formerly Covadonga), en route from Spain to Brazil in the late 1940s. They become embroiled in investigating mysterious on-board deaths, a secret microfilm, and hidden Nazi gold. The series starts with a mysterious woman called Luisa asking for help from the sisters, who smuggle her on board. Later Luisa is apparently thrown off the ship into the sea, and thus the investigation starts. It seems to finish quickly when someone confesses but their suicide in confinement is suspicious. Eventually the sisters' father proves to be alive, having been thought dead for the past two years. Complications continue as the sisters must choose who to believe - their father or their uncle - concerning the sending of people to concentration camps in trucks belonging to the family business.