In 1988, in Philadelphia, Police Detective Locke and his partner Maddox hunt down a female serial killer. Locke kills her in the subway and the case is closed by his chief Holt without identification of the killer. In 1997, similar crimes happen and Locke and Maddox believe in a copycat. However Locke finds that the killer is the same woman he killed nine years ago. Locke becomes obsessed with the case along the years and Locke believes she travels in time in the opposite time-line. When the woman reappears nine years later, Locke is waiting for her.