Young at Heart

A psychotic criminal from one of Mulder's past cases, John Barnett, is back to get revenge on Mulder for incarcerating him. Before Barnett's release, a renegade doctor had found a way to reverse the aging process - using Barnett as his test subject. Mulder and Scully rush to catch the now-unrecognizable youthful Barnett before he carries out his threat to kill all of Mulder's loved ones. Guest starring Dick Anthony Williams and William B. Davis.