In the Joseon Era a mermaid named Se-hwa falls in love with the town head, Kim Dam-ryeong. Their love story ends tragically when they are separated and lose their lives. Before perishing, Dam-ryeong leaves behind artifacts and journals in hopes of preventing a similar fate in the future. Hundreds of years later in the mordern day, Se-hwa is reincarnated as a naive, supernatural mermaid named Guest. She encounters Heo Joon-jae, a smooth-talking and highly skilled con artist who is the reincarnation of Dam-ryeong. When Guest follows Joon-jae around modern-day Seoul, she struggles to navigate human norms while adapting to life on land. Joon-jae takes her in, initially interested in a valuable jade bracelet she wears. However, as they live together, he finds himself genuinely falling for her. Together with his loyal team of con artists, Jo Nam-doo and Tae-oh, the group navigates comedic cohabitation and dangerous forces tied to Joon-jae's estranged, greedy family. Guest doesnt know how to talk at all so he doesn’t know that shes a mermaid.*