Dax demonstrates a disappearing egg trick for Quark, who is unable to work out how it's done. Shortly after, she's called to Ops where Sisko tells her that a Trill science team is coming, and the leader of the team is Lenara Kahn. She turns down the offer of taking leave. After greeting the science team on board the station, she reveals to Kira that Lenara was her wife in a previous host (Let the fem-slashing begin).
Kira and Bashir explain to Quark how the Kahn symbiont in previous host was married to Dax in a previous host. Repeatedly. Bashir explains that in Trill society getting involved with a relationship from a previous life is a no no and results in exile, which will lead to the eventual death of the symbiont (fem-slashing: DENIED).
There's a reception for the visiting Trill. Worf makes scintillating dinner conversation. "What do Klingons dream about, Worf?" "Things that would send chills down your spine." Yeah. Fluffy bunnies, probably. Dax and Lenara interact and come to the agreement that they're mature adults and can handle being around each other without doing something detrimental to Trill society. Their post-conversation glances tell a different story (fem-slashing: back on!).
Later on, they work on modifying the Defiant for their science mission. Dax and Lenara end up alone together on the bridge, discussing their past-life relationship. Dax invites Lenara to dinner with her and Bashir. Unfortunately Bashir already had plans, but Dax convinces him to cancel them. Cut to Quark's bar where Bashir looks extraordinarily bored as Dax and Lenara chat animatedly about their past lives. Dax points out the two of them have more in common than their prior hosts ever did. Bashir's called off to tend to a broken leg, leaving Dax to admire Lenara's Klingon earrings. They hold hands, as one of the other Trill observes from afar.
The Defiant arrives at the coordinates where they're going to do the test to try to create an artificial wormhole. The first test is successful, and Dax and Lenara have a bit of a hug, something which doesn't go unnoticed by the other two Trill. Lenara and her brother have dinner, and he expresses concern re how much time she's spending with Dax (If he switches to a female host, does he become her sister? I guess so). Lenara, upset, storms out, but her brother follows her and says he'll take her word that nothing's going on.
Later on, Lenara drops by Dax's quarters
They carry out another wormhole experiment and send in a probe. Unfortunately this causes an explosion and the Defiant takes damage. There's a plasma leak in engineering, cutting them off from Lenara - Dax attempts a rescue over a force field, and pulls her to safety in a Jeffreys tube where they announce their undying love for each other.
Why haven't I seen any adverts for Doctor Who yet? Tsk.
Back on DS9, Dax drops in on the recuperating Lenara, to looks from her brother. Dax suggests that she stay on the station and they work on the wormhole theory together, which leads to them arguing at length over whether they can stay together - Lenara says she wants to go back to Trill and think about it, but Dax says if she does, she's never going to come back.
The next morning, Dax watches Lenara leave with the other Trill. Awww, so sad.