After a traumatic car accident, Lee Kangmin is living alone on Jeju Island without his memories of the past. Once considered a miraculous recovery case of retrograde amnesia, he is now one of the best neurologists in South Korea. Tormented by the ghostly memories of his dead fiancee, he is reluctant to open his heart out of fear it will get crushed again.

His desperation to maintain a shred of normalcy in his life peaks when he encounters Ariadne, whose presence forces his painful memories to break free. On the surface, she appears to be nothing more than a naive foreigner but what he doesn't know is that she's a mythical selkie from Scotland. Centuries of distrust between their races return as they learn to live alongside each other.

Their love is tested by the gods, their people, and their past as Manannán mac Lir, the god of the seas, threatens to uproot their worlds as they know it. Together, they must reforge the broken bonds between their species in order to preserve their relationship and break the selkie's curse.