Ai-oon's identical twin Ob-oom is in a tragic accident the night of her wedding. Ob-oom survives but is left in a coma and her husband doesn't make it. Helpless to do anything for her sister, Ai-oon resolves to do her the favour she'd refused hours earlier. This leads her to a woman she could not have prepared for her, a woman she finds herself drawn to even as she questions whether she could have been involved in Ob-oom's accident.

May reminds Ai of their first real meeting.

Ai and May confirm their love. Oom wakes up from her coma.

Jan, Ob-oom's best friend, tries to discover the truth behind the accident that happened to Ob-oom and her husband. Meanwhile, Ai-oon begins to get caught up in her attraction toward May.

Ai-oon realizes how small her position is in her grandmother's heart compared to her twin, as she also has to face complicated feelings between falling in love with May and realizing that May's love isn't for her, but for Ob-oom.

Ai-oon goes on a date with May.

Jealousy ensues when exes are visiting

Aioon and May inspire each other to face their fears

Ai and May go to a party. Heartbreak follows after some misunderstandings.

Ai makes a heartbreaking decision. May fights for Ai. Oom is trapped between the two.

Ai and May finally reveals all their shared secrets. Oom is heartbroken. Ai makes a sacrifice for her sister.

A happy ending with a wedding.