Three women share a close bond that was deeper than any friendship. Song-ah, Senna, and Hyun-ah were both the same age and went to the same school. Song-ah was an especially giving friend who would do anything for a friend. She absolutely trusted Senna and treated her like a sister along with her twin sister Hyun-ah. She thought they would always maintain a close relationship. But she had no idea that Senna was planning revenge.