'Kingdom' Season 2 sees Lee Chang being betrayed by someone very close to him in a surprise for everyone
Spoilers for 'Kingdom' Season 2
The second season of 'Kingdom' sees Crown Prince Lee Chang (Ju Ji-hoon) get betrayed by his closest confidante. When Chang arrives at Gyeongsang, he learns from Lord Ahn-hyeon that the people at Gyeongsang already knew that he was about to arrive with his allies.
Someone among them was leaking information and Chang has a feeling that it is his guard Mu-yeong. He even confronts the man one night after a tough battle with tens of zombies and asks him if he is also revealing secrets to the Haewon Cho Clan. When Mu-yeong gets offended and tells Chang that he is the man who left his family and his pregnant wife only to accompany the crown prince and keep him safe, Chang lets it be.
It is not that his doubts have diminished after the confrontation, but just that he doesn't want to lose the one man who has been with him since the beginning of his fight -- against the Haewon Cho Clan's Hak-ju and the zombies, and so doesn't want to lose the only friend that he has. This need to keep some people close to him turns costly for Chang as it turns out that it was Mu-yeong who betrayed him.
From Gyeongsang, Chang decides to head to Mungyeong Saeje, the stronghold of the Haewon Cho Clan and where Hak-ju is currently located. Chang decides to attack him, as there are less number of men guarding the walls of Mungyeong Saeje, and attempt his removal.
This would help him lay claim to his throne and as a result would also help him save the people who are being infected by the plague increasingly.
However, he ends up walking into a trap set by Hak-ju who has been informed of Chang's plans by Mu-yeong. It becomes a tense situation where Chang gets locked in with his father, the King of Joseon, who is also infected by the plague. That leaves Chang with two options -- to kill his father and commit treason or get killed and turn into a monster himself. He chooses the former and this becomes the perfect excuse for Hak-ju to frame Chang as a traitor.
Mu-yeong, on the other hand, is being forced to work as a spy because his pregnant wife is being taken care of by the Haewon Cho Clan. If he hesitates in following their orders, his wife will be unsafe and that is what leads Mu-yeong to do as he does. We also see why Mu-yeong's betrayal hurts Chang as much with a peek into the past when Mu-yeong promised his loyalty to the prince for the first time.
Despite initially betraying Chang, when Mu-yeong learns of the Queen's evil plans of abducting pregnant women in the hopes of stealing one baby that could serve as a prince, Mu-yeong tries his best to inform Chang. Mu-yeong gets killed in the process, but somehow manages to reach Chang in time to tell him about the Queen's plan. In death, Mu-yeong gives Chang the one thing that could really help him overthrow the Queen.
'Kingdom' Season 2 episodes can be streamed on Netflix.