Set in the Joseon period. The king falls ill to smallpox and rumors start to spread that he has actually died. Meanwhile, Crown Prince Lee Chang is labeled a traitor by the Haewon Cho Clan, the clan of the current pregnant Queen and her father, Cheif State Councilor Cho Hak Joo. While trying to uncover the mystery of what happened to his father, the Crown Prince goes with his guard, Moo Young, to Dongnae to look for Physician Lee Seung Hui who treated his father, only to be stuck with Assistant Physician Seo Bi and the mysterious man, Young Shin, in a village plagued with a mysterious disease. The second season centers on the advancement of the plague across several provinces. In the lead-up to halting the outbreak, a devastating revelation ensues at Sangju. Upon the arrival of the winter season, the undead hordes now roam freely due to a change in ambient temperature. Fearing the ramifications of an imminent invasion, Prince Lee Chang attempts to garner support from his allies to stop the undead and reclaim his right to the throne. Unbeknownst to the Prince, another conspiracy for political gain is brewing within the corrupt Haewon Cho Clan. As Queen Consort Cho schemes to steal a male newborn to cement as heir to the royal throne, she further orchestrates a last ditch strategy to use the plague against the citizens of Hanyang, if her former plan fails to succeed. As calamity looms among the living, only one question remains. Can the Prince save his people in time and end the political turmoil at the capital or will the plague mark the end of the Joseon dynasty?