“Blood Oath” is episode nineteen of season two of Star Trek: Deep Space Nine.
Three Klingons arrive on DS9. They all have a connection to Dax, in the form of her previous host, Curzon, when all four of them swore a blood oath to hunt down a Klingon called the Albino.
The Albino had been raiding Klingon colonies, and the three were the captains of the three ships sent to stop him. Which they did, and in return he killed their first born sons, one of whom was Curzon’s godson.
Now, the Albino has finally been found, and they are going to go and attack him. They aren’t certain they wasn’t the newest Dax to accompany them, though. For one thing, agreements with a previous Trill host don’t carry forward to the next one, so Jadzia isn’t obligated to help. She does, however, want to. Which causes some problems with Sisko – Starfleet personnel aren’t supposed to go off on vengeance trips.
Jadzia has to decide if she wants to go, convince the Klingons to take her with them, and deal with the potential fallout of actually going off with them.
The three Klingons are all characters, played by the same actors, from TOS. Kor, from “Errand of Mercy”, Koloth from “The Trouble with Tribbles” and Kang, from “Day of the Dove”.