He was born as the son of Queen Park, the queen consort. Despite already having a crown prince, Queen Park insisted on educating her son Lee In, saying, 'You will succeed your father as the monarch.' Seeing his half-brother Lee Seon, who treated him kindly, young Lee In, troubled, made a vow: he would serve his brother with loyalty until the day he died.
Lee In's vow shines through when he becomes a hostage in the Qing Dynasty as a result of the invasion. While faithfully serving his role by sending regular reports to his mentor Kang Hang Soun about Qing's situation and devising ways to avoid war, Lee In's loyalty is ironically illuminated as an ambition to usurp the throne.
(Source: Korean = NamuWiki || Translation = MyDramaList)
