When Detective Frank Rourke's penchant for operating in gray areas to fight crime raises the suspicion of LAPD brass, the department assigns untarnished cop Kyle Craig to pose as Rourke's trainee and report back on his off-the-book methods.

The rift between Kyle and Frank grows when Kyle refuses to adhere to one of Frank's morally ambiguous rules, but the pair must put aside their differences when they learn the notorious hitman known as "El Cucuy" is targeting members of the Russian mob in Los Angeles.