The Adversary ( episode ) A Federation ambassador brings newly - promoted Captain Sisko orders to take the " Defiant " on a patrol of the Tzenkethi border , where a destabilizing coup has just taken place , but everything is not as it seems . ( " Season finale " ) Summary . Teaser . " " Dad , there ' s something I ' ve been wanting to say to you for a long time and now that I finally have the chance , I ' m going to make it short and simple . . . " " The opening words in the wardroom from Benjamin Sisko ' s son Jake as he proudly places a fourth pip on his father ' s dress uniform , proclaiming him Captain Sisko . The two embrace as cheers erupt from the crew ; being congratulated by his colleagues and as Quark serves the champagne , Chateau Cleon , 2303 , Federation Ambassador Krajensky informs Sisko that a " coup " has taken place on the Tzenkethi homeworld . Sisko is to take the ambassador and the to that sector to remind the Tzenkethi of the Federation ' s presence on nearby colony worlds . In the " Defiant " s engine room , Captain Sisko orders Chief Miles O ' Brien to begin preparing the ship for combat in case the Tzenkethi start looking for trouble . As O ' Brien begins his work , he hears a noise in the engine room , but sees no one . Act One . In the " Defiant " s turbolift , Lieutenant Jadzia Dax asks Sisko if he has told Kasidy Yates about his promotion . Sisko says he hasn ' t , and that he barely had time to tell his father the news . Dax presses Sisko about his relationship with Kasidy , saying that the whole crew is curious . Sisko tells Dax that the next time he sees Kasidy , he ' s taking her to the seventh game of the 1964 World Series . Dax , amused by Sisko ' s response , concludes that he likes Kasidy . Arriving on the bridge , Sisko orders the " Defiant " to get underway . Not long after departing Deep Space 9 , O ' Brien is working in a jefferies tube . He hears the noise again ; then suddenly takes a great fright before Doctor Julian Bashir appears from another tube . He asks the doctor why he didn ' t answer his call ; Bashir explains that he was tying a new medical console into the main power grid . After Bashir leaves , a curious O ' Brien takes a look at what the doctor has done and seems impressed , saying it wasn ' t a bad job for an extension course . In the mess hall , Sisko tells his Chief of Starfleet security , Lieutenant Commander Michael Eddington , to keep the ambassador out of harm ' s way in case the Tzenkethi decide to engage the " Defiant " . Eddington again congratulates Sisko on his promotion , and mentions how he wanted to become a starship captain himself when he first joined Starfleet . On the bridge , Constable Odo picks up a distress call from Barisa Prime . The colony reports that it is under attack before the " Defiant " suddenly loses contact . Act Two . The " Defiant " sets course for Barisa Prime , and Sisko asks Odo to notify Starfleet Command of the situation . Dax tries to contact the , which is the closest starship , but to no avail . Odo reports that the communication system is malfunctioning . O ' Brien and Dax are dispatched to make repairs . In the jefferies tube , Dax and O ' Brien find several tendril - like devices working their way into the " Defiant " s systems . They are protected by force field s , making them difficult to remove . O ' Brien reports to Sisko that the devices are all over the ship , attached to almost every critical system . O ' Brien states that these devices were not aboard when the " Defiant " left Deep Space 9 , leading to the conclusion that someone on board is a saboteur . O ' Brien reluctantly informs Sisko about his encounter with Bashir in the jefferies tube earlier . Sisko insists that he is not accusing Bashir of sabotage , but still would like to speak with him . However , Dax comes up with an idea to find out for sure who placed the devices . On the bridge , Sisko notifies his crew of the situation . Dax scans the crew for tetryon particles , since the saboteur would have been exposed to them when the devices were installed . Dax points out that she and O ' Brien ' s scans have come up positive since they were exposed to the particles when they found the devices , meaning that if no - one else tests positive then they ' ll be the prime suspects . The senior staff tests negative , including Bashir , much to O ' Brien ' s relief . As Dax scans Ambassador Krajensky , O ' Brien talks with Bashir about their encounter in the jefferies tube , of which Bashir has no memory . The scan completes , and Krajensky tests positive . Suddenly , the ambassador changes form and escapes the bridge , revealing himself to be a Changeling . Act Three . The " Defiant " cloak s and Sisko orders Dax to bring the ship out of warp , but she cannot . O ' Brien cannot uncloak the ship and Major Kira Nerys reports that the ship ' s weapons are armed . The crew has lost control of the " Defiant " . Sisko orders Odo and Eddington to begin a search for the Changeling before he can do any more damage , but they are unable to locate him . Odo is confident that the Changeling is still on board , saying that he will not leave until his mission is completed . Sisko believes that the Changeling ' s goal is to start a war between the Federation and the Tzenkethi , speculating that the distress call from Barisa Prime was faked , and goes so far as to suggest that their entire mission was engineered by the Dominion . Knowing that the Changeling can impersonate anyone on board , Sisko orders all non - essential personnel to be confined to quarters and sealed in with force fields , and that no one be left alone . After issuing weapons and orders to the security officers , Odo tells Eddington how he has never found it necessary to fire a weapon or take a life throughout his career . In the middle of their conversation , O ' Brien calls for a security team to be sent to the engine room . Odo and Eddington arrive to find Dax unconscious . Bashir reports that she has a severe concussion and takes her to sickbay . On the bridge , Bashir tells Sisko that Dax will be unconscious for the next couple of days , leaving O ' Brien alone in his attempts to regain control of the ship . Sisko tells Kira that he cannot allow the Changeling to start a war with the Tzenkethi , and that if O ' Brien can ' t regain control of the ship , he ' ll have to destroy the " Defiant " . Act Four . Sisko briefs the crew on their mission : They will break into two - person teams , each one equipped with phaser rifles , and systematically sweep the ship for the Changeling . A Bolian security officer voices his suspicions that the Changeling could be anyone of them , and Sisko reminds everyone to keep their partner in sight at all times for that very reason , and orders that anyone spotted alone be escorted to the brig . The crew begins searching the ship . Eddington asks Odo where he thinks the Changeling might be , but Odo is unsure , unable to put himself in the Changeling ' s position since he does not know his own people that well . Meanwhile , while Sisko and another security officer are searching a jefferies tube , the Changeling suddenly attacks them . The security officer is knocked out , leaving Sisko to pursue alone . Having been alerted to the Changeling ' s position , the crew moves to intercept . Arriving in the transporter bay , the Bolian security officer fires in Sisko ' s direction , believing that he has spotted the Changeling . Kira arrives from the opposite direction and insists that she is who she says she is , despite the fact that she and her partner have been separated for several seconds . The Bolian continuously accuses Kira of being a Changeling , and is paranoid to the point of ignoring a direct order from Sisko to lower his weapon . Just then , Odo appears and knocks out the Bolian . Eddington appears a split second later from Kira ' s direction , leading Sisko to conclude that any one of them could be the Changeling . Odo notes however , that Sisko is bleeding and therefore could not be the Changeling , as material removed from a Changeline reverts to its natural form , and his blood is just that – blood . Sisko calls Bashir and orders him to meet them in the mess hall . In the mess hall , Bashir begins performing blood screening s of the crew . Kira and the Bolian security officer prove to be themselves , but when Bashir tests Eddington , his blood reverts to a gelatinous state . As he is escorted to crew quarters , Eddington maintains that he is not the Changeling . As Eddington is about to be forced inside the room , the adjacent door suddenly bursts open to reveal the " real " Doctor Bashir yelling for help . The Changeling that took Bashir ' s place morphs into the ventilation system and Odo pursues . A call comes in from the bridge notifying Sisko that the " Defiant " has entered Tzenkethi space . Act Five . Kira reports that the " Defiant " is twelve minutes away from a Tzenkethi settlement on M ' kemas III . With this news , Sisko and Kira activate the auto - destruct sequence and set the timer for ten minutes . Sisko calls O ' Brien in engineering and asks if he has had any progress in regaining control of the ship . O ' Brien thinks he may have a way to shut down the force fields and deactivate the devices . As O ' Brien works , Odo and the Changeling – who is disguised as Odo – make their way into the engine room and each one tries to prove to the chief that the other is the saboteur . O ' Brien refuses to play " choose the Changeling " , and has the other officer in engineering keep his phaser on both of them while he deactivates the force fields . As the force fields deactivate , the Changeling drops his disguise and attacks O ' Brien and the engineering officer , leaving Odo to face the Changeling alone . As the two struggle , the Changeling tries to convince Odo to return to the Great Link , but Odo refuses and pushes the Changeling onto the warp core , fatally wounding it . Before he dies , the Changeling whispers something to Odo , which startles him . O ' Brien regains control of the ship . After Sisko and Kira abort the auto - destruct sequence , the " Defiant " leaves Tzenkethi space and heads back to Deep Space 9 . In the wardroom , Sisko tells the senior staff that the real Ambassador Krajensky disappeared on his way to Risa . Starfleet Security believes that he has been kidnapped , or possibly killed . Bashir asks about the " coup " on the Tzenkethi homeworld , to which Sisko responds that it never happened . Odo joins the meeting and informs Sisko of the Changeling ' s dying words : " " You ' re too late . We ' re everywhere " . " Memorable quotes . " " You ' d be surprised . People don ' t enter Starfleet to become commanders . Or admirals , for that matter . It ' s the captain ' s chair everyone has their eye on . That ' s what I wanted when I joined up . " " " " Why are you protecting these solids ? You don ' t belong with them . You belong with us . Let go . Don ' t you see ? You ' ve lost . It ' s too late for you to help them , but it ' s not too late to help yourself . Link with me , Odo . We can escape together . " " " " I . . . don ' t . . . think . . . so ! ! " " " " Getting jumpy in your old age , O ' Brien . " " " " Oh , " JULIAN ! " " " " Dad , there ' s something I ' ve been wanting to say to you for a long time and now that I finally have the chance , I ' m going to make it short and simple . Congratulations , " Captain " Sisko ! " " " " Now that you have another pip on your collar , does that mean I can ' t disagree with you anymore ? " " " " No , it just means I ' m never wrong . " " " " This calls for a toast ! " " " " That better not be from a replicator , Quark . " " " " Chateau Cleon , 2303 – I already put it on your account . " " " " Don ' t you trust me ? " " " " No , I don ' t . " " " " I know " exactly " how you feel . " " [ O ' Brien is faced with two Odos ] " " Look . I ' ve got more important things to do than play ' Choose the Changeling ' . Keep the phaser on both of them . " " " " Captain , there ' s something you need to know . The Changeling , before he died , he whispered something to me . " " " " Go on . " " " " He said , ' You ' re too late . We ' re everywhere ' . " " Links and references . References . 1964 ; 2303 ; Alpha Quadrant ; ambassador ; Autarch ; Barisa Prime ; blood ; Bolian ; centimeter ; Chateau Cleon ; concussion ; cortical analeptic ; " coup d ' etat " ; ; Dominion ; Dominion cold war ; duridium ; Engineering extension course ; Entebe ; expanding energy pulse ; Federation ; Federation - Tzenkethi border ; Federation - Tzenkethi War ; Founder ; Helaspont Nebula ; holosuite ; Jefferies tube ; kayaking ; M ' kemas III ; ore ; power grid ; promotion ; radiation poisoning ; replicator ; Risa ; sabotage ; shield generator ; ; Solais V ; Starfleet ; Starfleet Command ; Starfleet Security ; tetryon ; toast ; tricorder ; Tzenkethi ; Tzenkethi autarch ; Tzenkethi homeworld ; Tzenkethi warship ; ; warp plasma conduit ; World Series ;