The body of Yoon Seol Hee disappears at the National Institute of Scientific Investigation. Detective Woo Joong Shik seeks clues on her disappearance, while her husband Park Jin Han claims she is alive.
Yoon-Hee lives with her teenage daughter Sae-Bom. On a winter day, Yoon-Hee receives a letter from Otaru, Japan. Sae-Bom accidentally reads the letter and learns about her mother's first love, which she never spoke about before.