Ok Chanmi's twin, Park Wonseok, falls to his death at school. Chanmi transfers to her brother's school, Yongtan High, where she meets Ji Sooheon, a witness to her brother's death. Chanmi begins to explore the unsolved mystery of her twin brother's death.
Dan Chase absconded from the CIA decades ago and has been living off the grid since. When an assassin arrives and tries to take Chase out, the old operative learns that to ensure his future he now must reconcile his past.