Selah Cardi is a former marine biology student who woke up in a romance novel as an inconsequential extra. Eager to survive the plot, Selah manages to rescue Maria so that she and Duke Herbert, her fiancé, will be indebted to her. But then Admiral Ellaim notices her and her magical abilities that allow her to breathe underwater. Selah soon discovers that Ellaim is a merman called a siren, and that he needs her powers to recover from a mysterious illness. Will her dream of retiring by the sea in peace ever come true?