The Defiant crew discovers their descendants on a planet.
The Defiant investigates a planet inside an unusual energy barrier and finds a colony of about 8,000 people descended from its own crew. The colonists explain that when the ship tries to leave the next day, the barrier will hurl it 200 years into the past, where it crashes and the stranded crew builds their society. Kira died weeks after that crash, but an aged Odo survives, along with Dax in a new host, Yedrin, and the older Odo admits he has loved Kira for centuries.
The crew must choose between their own lives and the existence of their descendants. Yedrin offers a trick that would only repeat the crash, and the crew eventually agrees to relive history anyway. Instead the ship escapes, and the colony vanishes: the older Odo secretly changed the flight plan to save Kira. The fifth-season episode turns a time paradox into a moral dilemma and pushes Odo's feelings for Kira into the open.