Season synopsis
Contains spoilers for this season and earlier seasons.
In Seoul in 1987, student Eun Yeong-ro hides Im Soo-ho in her women’s dormitory, believing he is an injured activist. He is a North Korean agent, and his return with armed comrades turns Hosu University into a hostage site. Soo-ho keeps Yeong-ro close because her father, ANSP director Eun Chang-su, is leverage, yet struggles to treat her only as a means to escape. Detective Lee Gang-mu, captured while pursuing Soo-ho, searches for a way out and suspects the South Korean officials surrounding the dorm have their own plans for the hostages.
The agents and students learn the government’s public account is false and officials intend to exploit the standoff during the election. Yeong-ro discovers Soo-ho’s role and blames him after her brother Yeong-u dies following a clash at sea. Soo-ho repeatedly protects her, then joins Gang-mu in resisting the plan to sacrifice everyone inside. They try to expose the political scheme as ANSP officers Ahn Gyeong-hui and Tae-il maneuver to preserve power. Dormitory phone operator Gye Boon-ok, who has fed information to Ahn, learns he framed her sister Yeon-ok as a spy; she begins to question her allegiance.
After orders to kill the agents and hostages, Cheong-ya returns with money and an escape route. Soo-ho gives Yeong-ro his sister’s necklace as they part, but the escape plan collapses: Man-dong reveals he is a spy and kills Eung-cheol and Gyeok-chan, then is shot while shielding Soo-ho. Soo-ho returns to help Gang-mu release the hostages, then stays as SWAT closes in. He is shot protecting Yeong-ro and dies after giving her a recording of his last words. The scheme is exposed, Chang-su and other officials are imprisoned, and Yeong-ro listens to Soo-ho’s tape in their first-meeting café.