Best friends Taeyeon and Tiffany reunite on the adult world after their separation in high school. Feelings blow, and a promise is made. Another session comes, and the promise is changed. The Thirty Year Promise comes to light in a satisfied result.

Taeyeon slept the night before her wedding day. She woke and lived a single woman, and her partner a mere attractive stranger.     Taeyeon knows she is not hallucinating. She's going to marry Tif

On the day where Kim Taeyeon will finally see her one true love aka superstar Tiffany Hwang, she had actually met the dazzling girl before the concert; specifically, when she was at the airport.

Two people are tied by the red string of fate. Their souls are compatible to each other, hence the name "Twin Soul". Tiffany sees these strings of fate. What will she do about her nonexistent ones?