The Joining - S4.E13

When a transport ship crashed and wiped out the colony on Venus, Capt. Miles Davidow (C. Thomas Howell) was the sole survivor. But, after he's rescued by a team that includes his fiancee, Kate Girard (Amanda Tapping) and Scott Perkins (Jeffrey Jones), it soon becomes clear that Davidow did not escape unscathed. Removed from the high radiation atmosphere of Venus, his body is reacting to the Earth's air like that of a chemotherapy patient. When doctors give him the radiation his body seems to crave, strange things start to happen. Davidow's body begins to spawn duplicate parts - a hand, a torso and more from wounds that miraculously heal. In spite of this, Miles and Kate get married while he's still in isolation, but his time on Venus and the strange creatures he encountered there have had a profound change on Miles.