After being stranded on an uninhabited island for 15 years, Mok-ha is found by Kang Woo-hak, a man who reminds Mok-ha of her childhood friend. Cha Hak-yeon, also known as N, plays Kang Woo-hak in Castaway Diva.
When he was in high school, an accident made Woo-hak lose all his memories. He did not even recognize his family. His parents and brother loved him and cared for him, so he accepted whatever his parents told him as the truth.
Kang Woo-hak is now a journalist in his thirties, but he still refuses to live apart from his younger brother, Bo-geol. He not only insists on sharing a room with him but also emulates him in everything that he does.
Questioning his identity
Woo-hak goes to an uninhabited island with his brother and finds Mok-ha there. They bring Mok-ha to Seoul and get her help. Bo-geol asks Woo-hak to not make Mok-ha’s story public, but Woo-hak still does it, as he is rebellious and always does the opposite of whatever his brother tells him.
Initially, Woo-hak accompanies Mok-ha to her hometown because he wants to know her story better. However, when he finds out what she has been through, he decides to help her reenter society. He even allows her to stay at his family home.
Woo-hak reminds Mok-ha of her childhood friend, Ki-ho. Apart from that, when Woo-hak finds out that Ki-ho’s mother used to tell him the same thing that his mother tells him, Woo-hak starts believing that he might be Ki-ho.
He thinks that his family has been lying to him about his past for years. Although Bo-geol repudiates his assumptions, Woo-hak refuses to believe him. He helps Mok-ha meet Ran-joo, as he thinks that Ki-ho would have done the same after reuniting with Mok-ha.
The truth about Woo-hak’s past
Woo-hak becomes Mok-ha’s friend, so when Ki-ho sends her flowers, Woo-hak is disappointed to know that he is not Ki-ho. However, that very day, he remembers something from his past that makes him doubt his identity once again.
A memory of Ki-ho’s father, Mr. Jung, leads to Woo-hak finding out that Mr. Jung sent Mok-ha flowers to find Ki-ho. As Woo-hak remembers being on the receiving end of Mr. Jung’s anger, he comes to the conclusion that he was right about being Ki-ho.
He starts following Mr. Jung and stakes out his house. When he breaks into his house, he realizes that he has been there before. He also finds a family photograph of Mr. Jung, himself, Bo-geol, and their mother.
Bo-geol is then forced to give Woo-hak an explanation. He confirms his suspicions of him being Ki-ho and tells him that Mr. Jung hit Woo-hak when he disrespected him, and Woo-hak lost his memory. Their mother got them new identities and married the man they now know as their father.
She decided to hide the truth from Woo-hak because she believed that this is an opportunity for him to start afresh. While Woo-hak is grateful to his parents, he wishes to stop hiding. He wants to get his real identity back.
Woo-hak decides to talk to his father about his past. It is then that he comes to know that he is not Ki-ho. Bo-geol is Ki-ho, whereas Woo-hak is Jung Chae-ho, Ki-ho’s brother who lost his memories after getting hurt by Mr. Jung.
