The exploits of FBI Special Agents Fox Mulder and Dana Scully who investigate X-Files: marginalized, unsolved cases involving paranormal phenomena. Mulder believes in the existence of aliens and the paranormal while Scully, a skeptic, is assigned to make scientific analyses of Mulder's discoveries that debunk Mulder's work and thus return him to mainstream cases.
When a detective mysteriously uncovers the remains of an FBI agent who disappeared in the 1940s while investigating a similar murder case to one she is now on, Mulder and Scully believe that the original killer had passed his genetic trait of violence to his grandchild.