“To the Death” is episode twenty-three of season four of Star Trek: Deep Space Nine.
The Defiant returns to DS9 after helping a Bajoran colony to discover that the station has been attacked whilst they were away. A group of Jem’Hadar snuck onboard and stole a bunch of things. The Defiant pursues them through the wormhole into the Gamma Quadrant.
There, they discover a damaged Jem’Hadar ship. There is a Vorta on board (Weyoun; Jeffrey Combs playing yet another Star Trek role) who tells Sisko that the Jem’Hadar who plundered the station are renegades. A team had discovered an Iconian Gateway (such as was discovered in The Next Generation episode “Contagion”) and the Jem’Hadar rebelled and took control of it.
It is in both the interests of the Dominion and the Federation to stop the renegades and destroy the gateway, so a rather uneasy alliance is formed.