In 2790, centuries after the multibiosphere Ark launched carrying the last of Earth's humanity, friends Devon (Keir Dullea), Rachel (Gay Rowan) and Garth (Robin Ward) discover that the craft is on a collision course with a sun. Now they must find a way to save mankind. Exploring biospheres beyond their own, the three encounter other inhabitants for the first time as they search for a way to change the Ark's devastating fate in this sci-fi series.