Lee Mi Jin is a job-seeker who has been exhausted from working various part-time jobs and preparing for a job for a long time. One day, due to an incident, she ages into her 50s, causing her to live as a 50-year-old by day and rejuvenate into her 20s by night.

She is undeterred by this absurd tragedy and uses it as an opportunity to knock on the door of a job. With her wealth of experience from years of job hunting in her 20s and her seasoned 50s, she succeeds in landing the job she's always wanted.

Meanwhile, Gye Ji Woong, a sensitive and cranky perfectionist prosecutor, finds himself unwillingly involved with Lee Mi Jin day and night...