Ashin of the North is a sidequel from season two and a backstory about the mysterious character Lee Chang's group encountered on their journey north to discover the origins of the infected. In this eagerly anticipated bonus story, Ashin will unveil the mystery behind her identity. The new story will detail what had happened to Ashin in the past in the northern region and how the two characters' fates intertwined.

With the palace painted red with blood, Prince Chang is forced to pursue a risky strategy. Seo Bi takes the baby and hides.

To save innocent lives, Prince Chang and his men take over Hanyang. The queen determines that if she can't have the throne, no one can.

Seo Bi shares a critical discovery with Prince Chang, who has a favor to ask of her. Jo Hak Joo visits the queen and demands she tell him the truth.

When Jo Hak Joo is taken from his custody, Prince Chang goes after him. Seo Bi looks for a way to treat the disease. The queen awaits her prince.

After Prince Chang breaks into Mungyeong Saejae, a nightmare unfolds. Officials search the queen's home, suspecting she is hiding something.

An unexpected setback in Sangju poses new problems for Prince Chang and the others. Seo Bi and Jo Bum Pal seek safety with Jo Hak Joo.