The plot follows a class of high school students attempting to overcome the stress of being ranked by their exam grades, and facing the difficulties of being a teenager in a high-pressure, corrupt system.

Its central protagonist is Ra Eun-ho (Kim Se-jeong), a cheerful and kind-hearted 18-year-old who dreams of being a webtoon artist but is caught up in the search for a mysterious troublemaker in the school, known as 'Student X'.

Hyun Tae-woon (Kim Jung-hyun) is the son of the director of the school who enjoys his youth but hides deep scars.

In May 2017, KBS offered the leading role to Kim Yoo-jung as a follow-up project to her popular series Love in the Moonlight (2016).

[8][9] The first script reading of the series took place on June 19, 2017 at the KBS Annex Building in Yeouido, Seoul, South Korea.