The Age of Shadows (2016) on Netflix

Plot summary

Korea is under Japanese rule in the late 1920s, and Lee Jung-chool works for the Japanese police even though he once belonged to the independence movement. His superiors order him to get near Kim Woo-jin of the Heroic Corps and report on the group. Hashimoto is assigned as his partner, though Hashimoto's actual job is to watch Lee. Lee and Kim feign a friendship, and in Shanghai resistance leader Jung Chae-san urges Lee to help move explosives into Korea for a strike on Japanese facilities. Lee agrees to serve both sides, and the group boards a train for Korea with the explosives.