A married couple suddenly finds themselves living entirely different lives after their fates magically change through an unexpected incident.

A police detective from 1986 travels in time to the present to save his daughter.

Dae-soo and Mi-ra have Ah-reum when they are 17. Ah-reum is diagnosed with progeria, and as his body rapidly ages, his finds comfort in writing a story about how his young parents fell in love.