History of the Salaryman

One night Yoo Bang (played by Lee Bum Soo) enters a dark, mysterious villa with nothing but a flashlight, only to find an executive of the Chunha Medical Group, Ho Hae slouched in a chair, dead and Jin Ho Hae's niece, Yeo Chi (Jung Ryu Won) hiding behind a curtain. At Ho Hae's funeral, Yoo Bang and Yeo Chi are suddenly taken into custody for his murder. We're taken three months into the past to reveal what led to this murder and exactly who was responsible. During this flashback we meet Choi Hang Woo (Jung Gyu Won), a director from Ho Hae's rival pharmaceutical company, who is undercover to steal the formula for their new drug and the Chief Researcher from Chunha Group, Cha Woo-Hee (played by Hong Soo Hyun). The lives of these individuals will all be intertwined within these three months to reveal exactly just who murdered Ho Hae, and why (Source: Dramafever)