Because she has to go to work, Jung-eun leaves her baby daughter to her mother, Soon-ok, to babysit. However, the baby falls off from balcony, when Soon-ok accidentally fell asleep. Jung-eun gets shocked after the tragedy, but eventually forgives Soon-ok who has been feeling guilty. However, Jung-eun coincidentally finds out that her mother was not in the apartment on the day of the accident, but actually she was meeting someone outside. Now she has to track down what really happened on the day of the accident.