A bunch of high school students who were returning back to the city after a field trip in Jeju. Among them were two good friends, Kyuhyun and Jin Hae. Kyuhyun has a crush on Jin Hae since middle school and he plans to confess his feelings for her. Unfortunately, before he could even do it, a terrible storm came. Jin Hae was cast out into the sea and drown. But some mermaids rescued her and she was reborn into a mermaid.

Two years have passed and Jin Hae couldn't remember what has happened before. Even her memories of where she come from was forgotten too until she spotted the handsome man she recognized before. She longed to be with him but there will be difficulties she has to face.