Park Jinyoung who has been suffering with his family's debt and daily expenses is now experiencing an amnesia due to a mild traumatic brain injury when he passed out in front of the car of Kim Haesung, the eldest child of the owner of a large engineering firm in South Korea. Thinking that she's partly responsible for it, Haesung tries to help recover his memories.

Yeseul knew Mark since she was 7 years old. He was just that boy that lives next door. But her perspective started to change when her last year in high school in GI Academy had a Mark Tuan in it.