DS9 Season 3 Episode 21 The Die is Cast

Plot

Garak and Odo have not been heard from on Deep Space Nine in several days, following their departure in a runabout to investigate an attempt on Garak's life. The crew of Deep Space Nine is alarmed when a large Cardassian–Romulan fleet suddenly decloaks and flies through the wormhole to the Gamma Quadrant. The fleet, under the command of Cardassian Enabran Tain and Romulan Colonel Lovok, aims to destroy the homeworld of Founders of the Dominion. Tain has offered Garak the opportunity to return from exile, and the two reminisce about their past together in the Obsidian Order.
Back on DS9, the senior staff view Tain's message laying out the Obsidian Order and the Tal Shiar's plans to cripple the Dominion. Vice Admiral Toddman admits that while the Federation doesn't condone the plan, they don't intend to stop it either and must simply hope they are successful but plan for the worst: he orders DS9 on full alert and the Defiant and its crew to remain at the station for its protection. Commander Sisko, refusing to abandon his crewmate, launches an unsanctioned mission to take the Defiant into the Gamma Quadrant to rescue Odo.
Tain instructs Garak to interrogate Odo for information about the Founders, using a device that inhibits his ability to shape-shift. Knowing that Tain will never trust him if he refuses, Garak reluctantly does so. As the device causes Odo obvious pain, Garak begs him to reveal anything of use, even if it's a lie. Odo confesses his desire to return to his fellow Changelings, and Garak deactivates the device.
When the fleet arrives at the Founders' homeworld, they find little resistance and open fire, but soon realize that the planet is abandoned and the mission was a trap. Suddenly, Dominion ships appear and engage the fleet, vastly outnumbering them. In the resulting battle, the Cardassian–Romulan fleet is annihilated.
Knowing that the battle is lost, Garak leaves the bridge of his ship to rescue Odo. They encounter Lovok, who reveals himself to be a Founder and assists Odo in escaping. He confesses that the Founders viewed the Tal Shiar and Obsidian Order as threats and helped push Tain's plan forward in order to destroy them, meaning the only threats left are the Federation and the Klingons. He invites Odo to return to the Founders, but Odo declines.
Garak attempts to save Tain, but Tain refuses to leave, and Garak refuses to abandon him, so Odo knocks Garak unconscious and escapes with him on the runabout. Trying to escape the crossfire, they are badly damaged and fearing the end, Garak asks Odo for forgiveness. The Defiant then rescues them from the battle.
Back on Deep Space Nine, Toddman confirms there are no signs of other survivors from the attack, and subtly commends Sisko by deciding not to court-martial him. Garak sits mournfully in the wreckage of his shop. Odo arrives and invites Garak to join him for breakfast.