Second Sight is episode nine of season two of Star Trek: Deep Space Nine.
Sisko has realised it’s the fourth anniversary of the events of Wolf 359 and the loss of his wife, Jennifer. Whilst wandering the promenade, he meets a woman and is attracted to her, but she wanders off whilst his back is turned. He is unable to find her, and asks Odo to help.
Also at the station is a Federation starship, the Prometheus, in which noted terraformer Professor Gideon Seyetik is planning to reignite a dead star. The Professor is rather full of himself and arrogant; fortunately, he also knows he’s rather full of himself and arrogant, so he makes a better impression than he might, as he admits this.
When Sisko is invited aboard the Prometheus, he meets the Professor’s wife – the woman he has met a couple of times on DS9. Only, the wife doesn’t recognise him at all, and Odo says that she hasn’t left the ship since it docked. So, who is this mystery woman who is identical to her, and whom Sisko is definitely attracted to?