The film fills the gap between the Yongsan Station ending and the Norway cabin from Believer. Brian escapes the hospital and teams up with Big Knife to get revenge on Rak. Meanwhile Won-ho keeps chasing the real Mr. Lee, and the story fills with unexpected deaths as the plots around Laika play out.
The key reveal is Rak's motive. The drug lord had killed his parents. When Rak finally meets the real Mr. Lee (Tzi Ma), the old kingpin offers to make him part of his new gang. Rak refuses and shoots him in the head.
The film then returns to the cabin in Norway where the first film ended. Rak tells Won-ho that since killing Mr. Lee he no longer wants to live. He reaches for his gun, and Won-ho is forced to kill him. This settles the gunshot the original left ambiguous.
The hidden meaning is that the partnership was always heading toward this point. For Rak, revenge was the only thing holding his life together. Won-ho catches his target but has to kill the one person who got him there.