In a ceremony in the station's wardroom, Jake Sisko (Cirroc Lofton) pins a new pip on the collar of his father's, Commander Benjamin Sisko’s, uniform marking his promotion to the rank of Captain. Visiting Ambassador Krajensky then tells Sisko that the Tzenkethi, an alien race with a history of hostility toward the Federation, have unseated their ruler, the Autarch, in a coup d'etat; Sisko, a veteran of Federation/Tzenkethi conflicts, opines that the Autarch will not be missed, and while Krajensky concurs, he warns that the Autarch's replacement might renew anti-Federation hostilities. He says Sisko is ordered to bring the Defiant on a "saber-rattling" mission along the Tzenkethi border. Along the way, oddities occur on the ship and the crew suspects there may be a Changeling infiltrator. It is revealed to be Krajensky, but it is too late; he has already sabotaged the ship to the point it could instigate a war. After hours of searching, the crew tries to find the infiltrator with blood screenings but are unsuccessful. Sisko readies the ship's self-destruct while Chief O'Brien (Colm Meaney) tries to override the Changeling's systems. Constable Odo (René Auberjonois) fights the Changeling in main engineering and ends up killing him (becoming the first changeling to harm another). It is then revealed that the real Ambassador Krajensky was kidnapped and replaced (by his Changeling counterpart), the report of a Tzenkethi coup was false, and the entire affair was a Dominion plot to destabilize the Alpha Quadrant. Back at Deep Space Nine, Odo reveals the cryptic message the Changeling said before he died: "You are too late. We are everywhere."