Seven-year-old Ellie Prescott lives with her mother, Claire Langford, in a run-down rental room beside the railroad tracks in Aspen. On the night the story begins, the rental room is suddenly engulfed in fire, but Claire had already lost vital signs before the fire broke out. Panicked, Ellie holds her mother and keeps calling out to her, then picks up Claire's cracked-screen phone and calls her biological father, Nolan Prescott. At that moment, Nolan is at the luxurious Snowridge Hotel preparing to hold his wedding with Miranda Dalton. Ellie tearfully tells him that "Mommy won't wake up no matter what," but Nolan assumes his daughter is just making trouble on his wedding night, even tells her to "go find your mom if something's wrong," and then hangs up directly.
As the fire closes in, LUMI, a system only Ellie can see, appears. LUMI can only act after Ellie actively requests it, and it cannot directly revive the already dead Claire. It tells Ellie that there is only one way to bring her mother back: she must voluntarily leave the original world, live in another world for five years, and complete a task. Ellie accepts the condition, but still insists on finding her father before truly leaving, because Claire had told her to go to Nolan, and she at least wants to say goodbye to her dad and also wants him to go see her mother one last time.
