Toxic fumes spray out of an air conditioner and kills a man in his car. A bullet pierces through a man's brain vessel before he even gets to turn the ignition. A man picks up a phone and three stories of a building explodes. In the middle of all this chaos, four men walk out of the building without a scratch. They are the culprits of these heinous crimes. The foursome are Sang-yun, Jung-wu, Jae-young and Ha-yun. They're professional assassins for hire. Sang-yun is the cool-headed leader of the group, Jung-wu is the specialist in custom-made bombs, Jae-young is the unmatched sniper, and Ha-yun is the computer wiz. They're not your typical wise guys, but professional killers with a heart. They run a private business where people from all walks of life come to them and place an order. After they meet their clients and discuss the time, place and method by which they want their targets to be eliminated, they sign a formal contract. They even have a discount rate for students. Once the deal is done, they carry out their mission and finish it like a typical day at work. But one day, they leave a trail behind on a big job, and Prosecutor Cho hunts them down. While Prosecutor Cho is hot on their trail, Sang-yun meets a client and confronts a dangerous order he can't turn down. The client wants someone killed in the middle of a sold-out "Hamlet" play where high-profile businessmen, politicians and law officials will attend.