Sisko plans a daring mission into the Klingon Empire to find a Changeling.
Acting on intelligence from Odo that a Changeling has replaced Chancellor Gowron, Starfleet sends Sisko, Odo, O'Brien and Worf to expose the impostor. Surgically disguised as Klingons, they are flown by Gul Dukat in his captured Bird of Prey to Ty'Gokor, the Klingon military headquarters, posing as candidates for the Order of the Bat'leth. They carry devices meant to force any nearby shapeshifter into its liquid state.
General Martok sees through their disguises and has them jailed, then frees them after claiming he also suspects Gowron. Worf challenges Gowron to single combat, but Odo realizes that a Changeling would never risk an honourable duel and that the real impostor is Martok. The Klingons kill the exposed shapeshifter, and Gowron, realizing the Dominion had tried to trick the Federation into killing him, agrees to a ceasefire with the Federation. The episode was written by Ira Steven Behr and Robert Hewitt Wolfe and directed by James L. Conway.