A trill initiate named Arjin arrives on board DS9 to study under Dax. He and Bashir track Dax down in Quark's, where she's playing Ferengi games. And and Quark attempt to draft him into the game, but he protests he's tired.
The next morning, Arjin arrives at Dax's quarter's early and interrupts her with her wrestling buddy. What? She says Arjin needs to relax more.
In ops, O'Brien and Kira are Fixing things - apparently there's an infestation of Cardassian Voles, which look like mutant hairless critters. Hey, Dax, talking about yourself in the third person is a bit weird. Suddenly the runabout Dax and Arjin are flying about in is hit by a subspace pocket and some sort of mass embeds itself in one of the nacelles.
Kira and O'Brien work on ways to get rid of the voles. O'Brien comes up with a sonic pulse, but (un?)fortunately it turns out Ferengi are sensitive to it as well. Dax and Arjin's runabout returns to the station, and the pair go to dinner and Klingon opera.
O'Brien contacts the Cardassians about the voles, but doesn't get any help. Dax hands him a flute from Bashir with the note "It worked in Hamlin". Ha ha ha.
Dax tells Sisko that she doesn't think Arjin is suitable for joining, and he suggests she might like to talk to him about it.
The voles knock out the forcefield surrounding the subspace mass, and it starts glowing. Dax and Arjin set about analysing it, and she expresses her concern about his suitability as a host, he casts aspersions on her own suitability as host. Dax reveals to the other command officers that the subspace mass is a proto-universe which will expand to universe size. Dax's plan is to use a containment field to force a self-implosions.
Arjin, meanwhile, is drowning his sorrows in Quark's. Quark admits he was once an apprentice, and screwed up by having sex with the boss' sister. What a stirring pep talk!
Dax is concerned by the amount of technobabble emanating from the computer, and reveals to Sisko she's found evidence of life in the proto-universe. They suspend the containment field plan, in case it's intelligent life, and the expanding proto-universe blows a hole in the hull. Great! Kira asks if anyone has a plan, and Sisko says he'll think of something.
Meanwhile, Jake's in love with a Dabo girl. Riiiight.
Dax finds Arjin still drowning his sorrows in Quark's. He must be properly pissed by now. She tells him about how badly Curzon Dax treated Jadzia when she was an initiate. Also, Sisko may have come up with A Plan. They beam the proto-universe onto a runabout, and Dax and Arjin take it into the wormhole. They're forced to stop partway through because the containment field is collapsing. They very carefully recommence flight, avoiding all the verteron nodes, and emerge in the Gamma quadrant and return the universe to its subspace pocket.
Back on the station, Dax says goodbye to Arjin, and he leaves the station. The end.
Wait, what about the B-plot?! I want to know what happened with the voles! VOLES!