Kim Je Ha, a former mercenary known as "K2," becomes a fugitive after being falsely accused of murdering his girlfriend in Iraq. Returning to Korea, he takes a job as a bodyguard for Choi Yoo Jin, the powerful wife of presidential candidate Jang Se Joon. Je Ha’s true goal is revenge against Park Kwan Soo, Se Joon’s political rival, whom he believes was behind his girlfriend’s death.

As he protects Go An Na, Se Joon’s hidden and reclusive daughter, Je Ha forms a close bond with her. But his mission becomes complicated when he discovers that Yoo Jin—his boss and partner in revenge—is also the one endangering An Na.