In the movie The Policeman's Lineage, Min-jae comes from a family of policemen who have served the community for generations. He is a stern and upright officer who believes in the rule of law and upholding justice at all times. When he is ordered to investigate Kang-yoon, a skilled cop who leads an investigative team, Min-jae takes the job seriously.
As part of his mission, Min-jae joins Kang-yoon's team and begins to observe him closely. However, as he spends more time with Kang-yoon and witnesses his dedication to solving cases and bringing criminals to justice, Min-jae starts to question his own beliefs.
With each passing day, Min-jae finds himself becoming more and more like Kang-yoon - willing to bend the rules if it means catching the bad guys. He must now balance his loyalty to his superiors and his respect for Kang-yoon with his own conscience and the realization that sometimes breaking the law can be justified.
As the investigation deepens, Min-jae finds himself caught between his duty to uphold the law and his admiration for Kang-yoon. He must ultimately make a choice between his private mission and his loyalty to his colleague and friend.