Apocalypse Rising: The Federation launches a mission to Klingon space to expose Gowron as a Changeling.
Last time, the Changelings made Odo into a solid, and he realised that Gowron, head of the Klingon Empire, is a Founder.
Sisko and Dax are visiting with Star Fleet command to discuss the problem. The runabout arrives back at the station badly damaged. Sisko says Star Fleet's sending him to Klingon territory to try to expose Gowron.
"Captain! You're just in time for Happy Hour!" "Do I look happy?" Quark tells Sisko that Odo is very depressed. Odo is also holding a glass of urine. Oh, it's booze. He's a very depressed drunk. Sisko invites him along on the top-secret mission. They have a meeting and discuss how they're going to get into the massively defended Klingon military command and expose Gowron for a changeling. Sisko's been given some spheres which they think will make Gorwon revert to ooze.
They enlist Dukat's help and Bird of Prey. Sisko, Odo and O'Brien have been disguised as Klingons, and quite well too. Dukat is amused, and wants a holographic record. Dukat's first in command, Damar, thinks they should just nuke the site from orbit. The four faux Klingons have been listed for receiving the Order of the Bat'leth.
Also, Kira is pregnant. With Keiko's baby.
Worf attempts to coach his fellows in how to act like Klingons. Odo mopes about not being very convincing as a Klingon and gets told off by Sisko. The ship is contacted by another bird of pery who requests visual confirmation. Unfortunately the holoemitter which projects a fake Klingon is down, so Dukat has the other ship destroyed.
They arrive at the target base, but Dukat says he's not going to hang around - pointing out if they succeed, the Klingon war will be over, and if they fail... yeah. Cheery fellow. The four fake Klingons beam down and join in a drunken celebration in the Hall of Warriors.
Back on DS9, Jake and Bashir observe everyone seems on edge. Jake's worried about his dad, surprisingly enough.
The drunken celebration carries on through the night. Sisko beats up a Klingon who boasts about killing a Star Fleet captain. Martok wanders in, but doesn't appear to recognise anyone, until they go to set up the spheres. Then Martok thinks he recognises O'Brien but wanders off. The emitters are successfully set up, but a Klingon bumps Odo, and demands to know what the sphere is. Fortunately Worf covers for him, saying it's a Vulcan toy taken in a raid. Odo places the emitter as Gowron arrives.
Sisko is about to activate the emitters when he's called up to get his award. As Sisko steps down, Martok stabs him, revealing he knows it's Sisko. The four fake Klingons are locked up, and they try to convince Martok that Gowron is a Founder but, as it turns out, he already suspected as much. Martok says he'll release the four prisoners and help them reach the Hall of Warriors where they will kill Gowron. With Martok stabbing Klingons along the way, they reach the Hall, where he stops Odo from going in because he's not sure if the ex-changeling will be loyal.
Worf fights with Gowron. Outside, Odo realises it's Martok who's the changeling, and stops Worf from Gowron. The roomful of Klingons all open fire on Martok, killing him. They pretty much realise they've been had by the Founders, who intended Gowron to die and their fake Martok to take over the Empire. They manage to persuade Gowron to push for a cease fire.
Back on DS9, Bashir de-Klingons everyone. He offers to give Odo a different face, but Odo's happy to have his old one back