In an episode with a split personality that's probably even worse than "The Alternate's," Dax is assigned a Trill "initiate," Arjin (Geoffrey Blake), who she must help guide to the next step in the Trill symbiont-joining candidacy by offering her experience as a joined Trill. In the confines of this same character-oriented episode is a completely inappropriate plot centering around a "proto-universe," which Arjin and Dax inadvertently bring back from the Gamma Quadrant.
The proto-universe begins expanding, putting DS9 and (presumably) the entire Alpha Quadrant in danger of being destroyed—an overly large story idea that ends up making relatively little sense. Sisko decides he can't justify destroying a universe to save his own, so an alternate plan (putting Arjin's flight skills and plenty of technobabble to use, naturally) is concocted. The idea of an entire miniature universe with its own civilizations isn't bad in and by itself, and it even brings up some effectively interesting moments to ponder (Sisko's log about the Borg, first and foremost). But some non-addressed questions arise, like, for starters, how returning the proto-universe to "where it belongs" will keep it from expanding and wiping out the Gamma Quadrant (and beyond), and just how Sisko can have the arrogance to make a decision about the "universe" in a mere hour.
In any case, the whole premise of pondering the nature of universes doesn't at all belong in this small episode of character interaction, which, in a vacuum, is a good one. The writers supply Dax with some reasonable backstory, with the humorous notion that Curzon Dax was notorious for washing initiates—including Jadzia herself—out of the joining program. ("I'm not Curzon," Jadzia constantly reminds Arjin). The Sisko/Dax relationship is put to good use again with a believable dialog scene. Arjin turns out to be a fairly interesting character, and the dialog between him and Dax is nicely written. But forcing the tech plot and character story together is a mistake that the writers have already made too many times this season.