During the Joseon Dynasty, the Secret Royal Inspectors are the eyes and ears of the king. They travel the provinces undercover and listen to the plight of the common people, investigating abuses and corruption of government officials.

该剧讲述了关于韩国特有的职务暗行御史的故事，他虽然是百姓的嘴巴，是王的耳朵，但是却不显露自己，他们的职务是相当于帮现代人实现正义的人物，通过描绘朝鲜时代真正的暗行御史来向我们展现对于我们来说真正需要的英雄的故事。

Tae-ju, a murderer serving a life sentence in prison, is given a temporary release to save the life of a seriously ill young girl, Se-hee, who suffers from Wilson's disease and desperately needs a liver transplant. Se-hee is the daughter of Yeong-woo, and old friend of Tae-ju's who is now a police officer. Upon discovering that Se-hee's now deceased mother was his ex-girlfriend, Tae-ju realises that he is in fact her biological father, and does everything he can to try and save her life.