The story set in a universe where South Korea is a constitutional monarchy. The Empress regnant, already in her thirties, is still unmarried and without an heir, which prompts the imperial court to look for a suitable Crown Prince. They encounter Lee Hoo, the son of the empress' uncle, and brings him into the palace where he begins to learn the life of a royal. However, another competitor arrives at the court: Lee Joon, the son of another uncle of the Empress. They compete for the title of Crown Prince via a trial of several tasks to determine the worthy future Emperor of the country.

《四子》是讲述失去了心爱的男人的女警察偶然发现一对双胞胎后展开的悬疑浪漫推理剧。预计下半年开拍，播出平台未定。