Sia Tien is a strong mother who raises her child alone and is a key researcher in time-slip research based on parallel theory, developing a method of traveling through time using black holes. When Choi I-hoo kidnaps her son and demands that she hand over the new technology, Sia Tien uses the as-yet-unfinished time machine to go back in time two hours. While trying to save her son, meets 3 of her own selves.