A Bona fide Killer summary: When Yu Bona resumes her work after maternity leave, she defies the stereotype of a typical mother. She is tasked with a mission that requires her to travel to a rooftop, where she aims her sniper rifle at a hotel room nearby. This marks the return of the legendary assassin, "Kingfisher," with a lethal shot. As Bona's target list grows, her husband Taesung, who happens to be a journalist, is given the task of investigating the assassin's comeback. With the mounting number of casualties, the line between Bona's personal and professional life blurs.