In order to save Hyeon-su’s life, episode 4 of Black Knight begins with Sa-wol deciding to trade his second-place victory during the Deliveryman competition. Heyon-su advances to the following round while Sa-wol is eliminated because the Cheonmyeong Group isn’t interested in that sort of complication. Hyeon-su, however, is unable to proceed owing to her broken arm. To give the refugees a sense of hope, Sa-wol is brought back.
Ryu Seok is attempting to pull off a mass killing of the refugees by moving a select group of people to his recently developed district based on their bio-data and confidential personal information. He is attempting to populate a brand-new world using genetically superior people. Ryu Seok requests assistance from Seol-ah and the Defence Intelligence Command. Additionally, his supposedly well-intentioned father is not informed.
After receiving a clue from 5-8, Seol-ah keeps trying to look into men who have triangle tattoos. While this is going on, 5-8 and his group destroy a generating unit that is headed for District A.
Back with Sa-wol though, and he advances to the next stage of the competition. The mentor assigned to him is 4-1, and interestingly, no one is aware of their prior relationship. In the midst of all this, Sa-wol is also given some short-term accommodation.
Sa-wol gets ready to face Joo Gyeong-nam, one of the other finalists. The fight will occur within the Core District, where it’s actually possible to breathe. The fight will be airing live, and in exchange for the refugees’ attendance, both meals and compressed oxygen will be provided.
The episode cuts back and forth between the tournament’s finale round and 5-8 discovering Ryu Seok’s scheme in the districts at this point. Eventually though, the Delivery-man competition is won by Sa-wol. However, his metallic skull can be seen, owing to the cut on his forehead. While he is enjoying himself, Ryu Seok notices it.
5-8 rushes towards the districts but he is too late. Bombs explode in multiple refugee settlements, killing those living there.
Sa-wol achieves victory in the contest and is crowned the winner of the Deliveryman competition by the end, but the consequence for all this is that Ryu Seok ends up killing numerous refugees, with 5-8 taking too long in his attempt to save them.
The episode ends on a gloomy note. Sa-wol’s moment of personal triumph is balanced by Ryu Seok’s plotting and after such a devastating ending, it’ll be interesting to see how things develop from here on.