Once Someday

Jeong-Woo is sent to a sanitarium deep in the mountains to overcome his alcoholism. There he meets a young nun named Maria who has a special ability to see inside people. In this isolated sanitarium Maria is the only person who seems to care for him and soon he feels drawn to her. While struggling with his withdrawal symptoms, Jeong-woo has a vision where his reality is different from what he believes. The further he escapes from his alcoholism, the closer he gets to confronting the past that he has denied for years.

A 13 year old girl who lives with her widowed mother in a town in Korea. Somewhat withdrawn and living in dreams, her main dream is that her real mother is a famous pop singer. Soo-ah falls in with a delinquent schoolgirl, and after a tense argument with her mother, blurts out that she is not her real mother. She runs away on a train to Seoul to see her "real mother" at a concert and be with her.

Do-gyeong jumped in to save his student Ji-yong from drowning. After the two pass away, Myeongji, Do-gyeong's wife, and Ji-eun, Ji-yong's sister, are left alone in the world, having to cope with the loss of their loved ones. Myeongji travels to Warsaw, Poland, to avoid her harsh reality. She meets an old friend and hides her husband's death as if trying to reject the tragedy.

Mira in her late 40's has been living in Paris for around 20 years. Having just divorced her French husband, she decides to visit Korea, and meets her old friends Young-eun and Sung-woo. While having a cheerful time in the bar, Mira goes to the toilet and after she returns, time is reversed back to 19 years ago. It is the day of Mira’s farewell party, before she left to France.

Sun-joo is busy preparing for her upcoming wedding. But her fiancée Ji-hoon plans to go on a business trip with the beautiful writer So-ra who turns out to be Sun-joo’s best friend from before. With all the doubts and jealousy, she lies to So-ra and accompanies her in place of Ji-hoon. But on their way she realizes that the memory about their dearly friend Yeo-eun, who died in a tragic accident, are quite different. What really happened to them? Can they reveal the untold truth?