“Children of Time” is episode twenty-two of season five of Star Trek: Deep Space Nine.
The Defiant is on the way back to Deep Space 9, following a week-long reconnaissance mission in the Gamma Quadrant. Kira and Dax are looking forward to returning to the station. Kira has separated from Shakaar after they visited a shrine and they asked the Prophets whether they were supposed to be together. The response was they were not, so Kira and Shakaar separated. Odo excuses himself from the conversation; Dax says it’s because Odo finds that sort of conversation uncomfortable. It may actually have something to do with Odo’s feelings about Kira.
Dax picks up some readings from a nearby solar system, with an energy barrier surrounding the fourth planet. Dax wants to take a look – now, because the barrier’s strength is intensifying and they soon won’t be able to pass through it and there may be life on the planet. Sisko reluctantly agrees and they pass through the barrier, with a little trouble. Kira gets a shock during the passage. The ship is also stuck for a few days.
They receive a message from the surface, and it seems there are some inhabitants – humans. They know Sisko’s name, and more, and have been expecting him. Which is a little weird.
It gets weirder. The surname of one of the two people who greeted them is Dax. That of the other is O’Brien. This is not just a strange coincidence; the inhabitants state that they are descended from the crew of a Starfleet vessel that crashed on the planet two centuries ago. That ship was the Defiant. When they try to pass through the energy barrier in two days, they will be thrown back in time after they encounter a temporal anomaly and stranded. Where they will found the settlement they are now visiting. This all comes as a bit of a shock. The energy discharge that Kira suffered killed the Kira who went back in time.
Now they know about the accident, it should be possible to prevent it from happening. Which, according to Worf, will cause the timeline in which the Defiant got sent back through time will collapse, and everyone will cease to exist. The Dax who was on the crashed Defiant (well, the same Dax but 200 years older; time travel can be really confusing) has a plan to stop that from happening, by using what happened to Kira on the Defiant – she was essentially duplicated on a quantum level, so they are going to do the same with the Defiant. So, will the plan work?
There are lots of descendants of the crew on the planet, and this provides more weirdness for the crew. There is also Odo – the current Odo is unable to keep his shape due to the barrier, but the one on the planet can. This Odo finally discloses his feelings for Kira.
It all looks like everything is going to work out okay. So something is bound to go wrong. Which results in a bit of a dilemma.