The quartet of genetically engineered individuals from the episode "Statistical Probabilities" show up on the station, impersonating an Admiral and his staff. They help Julian Bashir refine a medical instrument so he can operate on Sarina Douglas.
The operation is a success and Sarina is able to speak for the first time in a long time, even going so far as to notice "everything." When she's reintroduced to the rest of her group, they immediately try to help her feel included by starting up a sing-a-long, which, at first, isn't too good until her true voice comes out.
The quartet has realized that the universe is going to be destroyed, in "60 trillion years, 70 at the most", and tries to work out a way of keeping it in balance while Sarina starts to argue against any such attempt. When Bashir comes in to check on her later, she's seated as she was before the operation was a success, and, fearing the worst, goes over to check on her to find that she was just playing the part they all expected her to play.
Bashir falls in love with her and assigns another doctor to take over her care so he can pursue her romantically. Miles O'Brien expresses his concerns to Julian. Indeed, Sarina is not ready for a relationship but feels pressured to thank Julian by being the woman of his dreams. At the end, she leaves DS9 for a scientific internship.