1782年,朝鲜正祖为了反对老论的势力,查办各地贪污,期间任命崔侧根(金明民 饰)为探正,他即是朝鲜史上出色的一位侦探。一位户房因为揭发贪污行为被杀,崔侧根巧妙的揪出了患有色盲症的真凶,然而凶手马上又被不明杀手用清国进口的铁针杀死,案件陷入了僵局。 崔侧根收用狗盗高手韩西弼(吴达洙 饰)为助手后,接下了调查烈女案的任务。老论首领任判书的侄女金贤英为贞洁自杀,她生前开辟高山乌头农场,宣扬平等理念,深得奴隶爱戴,金贤英死后,农场被交给美艳的韩商行(韩智敏 饰)打理,而韩商行也与清国铁针有着千丝万缕的联系。仇恨天主教势力的任判书和韩商行之间亦颇有渊源,贪污案和烈女案的线索交织,同时指向了韩商行……"Detective K" tells about the adventures of Joseon's top detective (Kim Myeong-min) as he investigates, as ordered by the King, a series of mysterious murders plaguing the country. During his secret mission, he meets Han Seo Pil (Oh Dal-soo) who eventually becomes his sidekick, and Han Gaek Ju (Han Ji-min), an influential business woman who is a key figure in the case. As they dig deeper into the mystery, they uncover disturbing secrets that link the murders to a massive conspiracy that will shake the whole nation of Joseon.