The Knight of Doom, adapted from the online cartoon Express Knight, tells the story of the air-polluted legendary courier "5-8" after he met April, a refugee who dreams of becoming a courier in 2071. Jin Yubin plays 5-8, a legendary courier with extraordinary skills from a refugee background; SSH plays Liu Xi, heir to Qianming Group, who is the villain in the play; Li Quan plays Major Xue'e, a military intelligence division, who saves lives in April; and Jiang Youxi plays a refugee who dreams of becoming a courier in April.