In an imaginary 'Joseon' where 'Sijo' (traditional Korean poetry) is the national ideology, the people who poured the hardships and adversities of life into Sijo and cast them aside, now live without freedom or happiness after Sijo activities are banned due to a treasonous incident. Then, the 'Joseon Sijo Challenge,' open to everyone, is held for the first time in 15 years. The secret Sijo group 'Golbindang,' which hides its identity behind masks and was formed to expose the wrongdoings of the nobles to create a happy world, sees this as an opportunity to bring a new wind to Joseon. Meanwhile, Hong Guk, the king's influential confidant and Grand Minister of Sijo, plots to capture Golbindang on the grounds that they are spreading malicious rumors about him...