The BAU team investigates a mass murder at an Internet security company in Charlottesville, Va., but clues reveal it is not a typical serial killer at work. Also, Prentiss must complete recertification training under Morgan's watchful eye.
Deep Throat tips Mulder to a critically important case involving a missing fugitive and the cloning of extraterrestrial viruses.
Kate's original crime that started her life on the run is revealed. Meanwhile, the survivors lay one of their own to rest, Kate sleeplessly watches over a feverish Sawyer, and Mr. Eko has a surprise for Locke regarding the hatch.
While investigating a rural religious cult, the agents expose a sinister experiment involving violent teens and alien DNA.
When Rousseau leads Sayid to a mysterious captive in the jungle, he becomes determined to find out if he is one of the "Others." Meanwhile, Sawyer discovers Hurley's potentially devastating breech of the survivors' trust and blackmails him into helping track an elusive island creature that won't leave Sawyer alone.