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
"Commander's log, Stardate 48959.1. It is with mixed emotions that I record this, my final commander's log. The last three years have been the most demanding, and rewarding, of my career. I can only hope that the future will hold even greater challenges."

"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…"

In the wardroom, Benjamin Sisko's son Jake 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 in two days to remind the Tzenkethi of the Federation's presence on nearby colony worlds, to "show the flag," as Sisko puts it.

In the Defiants 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
"My son, the writer, thinks that I should say something profound on this occasion. He even offered to write me a brief statement. I told him I'd take care of it myself, but as it turns out, the only thing I can think of is: Begin Captain's log, Stardate 48960.9."

In the Defiants 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 even 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 in the holosuite. 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 Sisko tells him that it really doesn't change anything as he already has the assignment and the crew he wants. Eddington notes that when people join Starfleet, they don't do so to become commanders or admirals but always set their eyes on the captain's chair, and laments that he isn't likely to ever do that. Sisko suggests that Eddington could apply for a transfer from security to command, but Eddington reassures Sisko that he's happy where he is.

"Captain's log, Stardate 48962.5. We are twelve hours from the border. I haven't been in this area since the last Federation-Tzenkethi War. Being here brings back a lot of memories, most of them bad."

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
"Captain's log, supplemental. We've been unable to re-establish contact with Barisa Prime. Therefore, I have no choice but to assume we are at war with the Tzenkethi."

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 Defiants systems. They are protected by force fields, 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 with a tricorder, since the saboteur would have been exposed to them when the devices were installed. Dax points out that her and O'Brien's scans have come up positive since they were exposed to the particles when they discovered 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, but Bashir denies he was there.

Krajensky's test is positive – and suddenly he changes form and escapes the bridge through the ventilation system, revealing himself to be a Changeling.

Act Three

The Defiant cloaks 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 phasers and photon torpedoes 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. In the Defiants mess hall, 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, depending on how long the Changeling was impersonating Krajensky, the entire basis for their mission may have been an invention of 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 to the security officers, Odo does not take one himself. He tells Eddington he has never found it necessary to fire a weapon or take a life throughout his security career; he also notes that no Changeling has ever harmed another. 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 assignments: 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 any one 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 Changeling 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 screenings 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 found 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 pointed 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 forcibly merges with Odo trying to convince him to escape and return to Great Link with him. Odo refuses and pushes the Changeling onto the warp core, fatally wounding it. Odo approaches and apologizes to the Changeling, who whispers something to Odo before he dies, turning into ash.

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.

"Captains log, supplemental. We've returned to the station without further incident. However, I'm concerned about my chief of security, who hasn't said a word since we left Tzenkethi space."

In the wardroom, Sisko tells the senior staff that the real Ambassador Krajensky was on his way to Risa for an extended vacation, but he never arrived. Starfleet Security believes that he has been either kidnapped, or possibly killed. Bashir asks about the coup on the Tzenkethi homeworld, to which Sisko responds that it never happened, and that Starfleet wants a detailed report from each the senior officers. Odo joins the meeting and informs Sisko of the Changeling's dying words: "You're too late. We're everywhere."

Memorable quotes
"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!"
 - Jake Sisko, at his father's promotion

"Well, 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."
"Oh, we'll see about that."
 - Kira and Sisko

"Curzon would've been proud of you, but not as proud as I am." 
"That means a lot to me, Dax."
 - Dax and Sisko

"Though I don't fully understand this humanoid obsession with rank and title, if anyone deserves to be promoted, it's you." 
"Thank you, Constable."
 - Odo and Sisko

"This calls for a toast!"
"That better not be from a replicator, Quark."
"Chateau Cleon, 2303 – I already put it on your account."
 - Quark and Bashir

"Here's to the newest and best captain in Starfleet, and all I can say is, it's about time."
 - O'Brien's toast to the newly promoted Captain Sisko

"Getting jumpy in your old age, O'Brien."
 - Miles O'Brien, to himself

"Oh, JULIAN!"
 - O'Brien, after the Changeling impersonating Bashir surprises him in a Jefferies tube

"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, but you don't get to be a Captain wearing a gold uniform."
 - Michael Eddington

"Don't you trust me?"
"No, I don't."
"I know exactly how you feel."
 - Kira and a Bolian security officer

[O'Brien is faced with two Odos]
"Look. I've got more important things to do than play 'Choose the Changeling'." (to an Ensign) " Keep the phaser on both of them."
 - O'Brien, when faced with deciding which shapeshifter is the real Odo

"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!!"
 - Changeling saboteur and Odo

"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'."
 - Odo and Sisko

Background information
Story and script
 The working title of this episode was "Flashpoint". In the Deep Space Nine Chronicles intro, it is stated that the episode was untitled until a contest was held and "The Adversary" was selected.
 The intention behind this episode was to create a thrilling installment. "It was meant to be a paranoid, tension-producing show," said Ira Steven Behr. (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 80)
 The producers had initially planned to do a show that had a cliff-hanger ending involving Changelings on Earth. The story was set to introduce Joseph Sisko and would take place in Starfleet Headquarters, with the end to revolve around Benjamin Sisko saying that the Founders had infiltrated the very heart of… and that was the end of the show. However, for reasons still unknown, Paramount nixed the idea, saying they didn't want a cliffhanger ending, and so the writers came up with a story about a Changeling wreaking havoc on the Defiant instead. As Robert Hewitt Wolfe puts it, "That's when the idea of the Defiant heading inexplicably toward destruction, like the death machine that she really is, being all locked down and going like a runaway train, became the basic hook that everyone really liked." However, the Changelings-on-Earth story later served as the basis for the episodes  and  the following season. ()
 The scene in the Defiants mess hall where the senior officers are taking blood samples of each other to determine which one of them is the Changeling is very reminiscent of one in the 1938 short story "" by  (under the pseudonym of Don A. Stuart), and its   film adaptation . However, the writers cite neither the original story nor the Carpenter film as their primary inspiration for this episode, but rather , 's  adaptation of the same story, which omitted the element of a shapeshifting enemy. Paranoia was something the writers were interested in exploring, as it was something rarely seen in the Star Trek universe. ()
 The writers decided to use the line "No Changeling has ever harmed another" as an important element in this episode. This line had been heard a few times already (in ,  and ), and its importance would return in the fourth season finale, , where Odo receives his punishment for killing a fellow Changeling.
 The character of Michael Eddington was deliberately set up as a red herring in this episode. The writers felt that the way actor Kenneth Marshall had portrayed the character in ,  and  had always implied some kind of underlying threat, so they decided to use that to their advantage in this episode. Indeed, after the episode aired, the word around the internet was that Eddington was a Changeling infiltrator, and that this was obviously going to have a bearing on the upcoming season. Upon hearing this, the writers decided that they would never make Eddington a Changeling. () Later on, it would be revealed that Eddington was a threat, but not in the manner people expected: he was a member of the Maquis who would eventually betray Starfleet.
 Sisko's opening log entry was not in the final draft shooting script.

Production
 The fight between Odo and the Changeling at the end of the episode was extremely complicated to put together due to all the morphing effects. Producer Steve Oster points out that there are more morphing effects in this short scene than in the entire third season. According to actor Rene Auberjonois, after principal photography was completed, all the cast were allowed to leave except himself and Lawrence Pressman. He explains that during the main shoot, he and Pressman had filmed the scene as normal, but to make sure the effects would work properly, each of them then had to re-enact the scene separately, looking at a monitor and matching their movements exactly. () There are actually some clips of both actors shooting the fight without the other present in the Deep Space Nine Chronicles intro to this episode.
 In the episode's trailer, the energy bolt that knocks Odo away after he pushes the Changeling against the warp core is omitted, leaving Odo seemingly knocked away by nothing.  
 The scene when Krajensky morphs into a Changeling and escapes through the vent is one of visual effects supervisor Glenn Neufeld's favorite shots from the entire seven years of Star Trek: Deep Space Nine.
 Kenneth Marshall commented that the episode was: "technically one of the more interesting shows I've done. It's fascinating how they do the morph sequences. I haven't seen them do the actual special FX, but they shoot it three different ways on the set. In the last shot, everyone tiptoes off the set so as to not disturb anything even a fraction of an inch." ()

Reception
 Ronald D. Moore was a big fan of this episode, particularly due to how it portrayed the Founders. "It […] represented an interesting way to use the Changelings, making them more of a threat," he said. (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 80) Another reason Moore approved of this episode was that he considered it to be very un-Star Trek. "It really appealed to me on this sort of visceral John Wayne level," he remarked. "There's a monster on the ship, it's after us, and we're gonna hunt it down and kill it. We're not gonna negotiate with it, we're not gonna worry about whether it's sentient, we're not gonna play any of the usual Star Trek games with it. It's just, 'Find and kill the monster.' There was something very pure about that show." ()
 Ira Steven Behr sees this episode as an important step in the show's movement towards serialization, which would reach a peak in the six-episode arc which opened season six and the nine-episode, ten-hour arc which acted as the finale of the series itself; ""The Adversary" was the first one where we really knew we were going to be starting to get the S-word, serialized, just a tad. In spite of all the finger-wagging and knowing we weren't supposed to, it was just a little bit, a little bit." (The Birth of the Dominion and Beyond, DS9 Season 3 DVD special features)

Trivia
 This episode marks the first appearance of several new sets aboard the Defiant, namely main engineering, the mess hall and the extended corridor set.
 According to the , the rifles used in this episode are the first rifles ever seen in Star Trek which actually have a trigger.
 In the teaser for the episode, Sisko is promoted to captain; however, in the opening credits of the show he is still credited as "Commander Sisko". This is the last episode to credit Sisko as a commander. It is also the last time Sisko is seen with hair and it is the last episode to have the original opening credits from Season 1, which were both first seen in the premiere episode, . In the  onward, Sisko is now bald and a new opening credits sequence is used.
 This episode marks the last time Alexander Siddig is credited as "Siddig El Fadil" as an actor. As a director, however, he remains credited as Siddig El Fadil for .
 According to Jadzia Dax, there are 47 people on board the Defiant'' in this episode.

Video and DVD releases
UK VHS release (two-episode tapes, CIC Video): Volume 3.13, 
As part of the DS9 Season 3 DVD collection

Links and references

Guest Stars
 Lawrence Pressman as 
 Kenneth Marshall as Michael Eddington 
 Jeff Austin as Bolian

Co-Star
 Majel Barrett as Computer Voice

Uncredited Co-Stars 
 Sam Alejan as Starfleet sciences officer
 Ivor Bartels as Starfleet operations officer
 Ivy Borg as Rita Tannenbaum
 Jeff Cadiente as Starfleet operations ensign
 Tory Christopher as Starfleet sciences lieutenant
 Kathleen Demor as Starfleet operations officer
 Terry Green as operations lieutenant
 Randy James as 
 Mark Lentry as Starfleet command lieutenant
 Dennis Madalone as Starfleet operations officer

Stand-ins and stunt doubles
 Tom Morga as stunt double for Jeff Austin
 Unknown stunt performers as
 Stunt double for Rene Auberjonois
 Stunt double for Nana Visitor
 Photo double for Rene Auberjonois

References 
1964; 2303; 2368; accusation; Alpha Quadrant; ambassador; Autarch; Barisa Prime; blood; Bolian; career; centimeter; Chateau Cleon; combat mission; command chair; concussion; cortical analeptic; coup d'etat; ; deflector shield generator; Distress caller; distress signal; Dominion; Dominion cold war; duridium; Engineering extension course; extension course; Entebe; evacuation pod; expanding energy pulse; Federation; Federation-Tzenkethi border; Federation-Tzenkethi War; Flag of the Federation; Founder; gelatinous state; Helaspont Nebula; holosuite; Jefferies tube; kayaking; M'kemas III; nonessential personnel; ore; power grid; prime suspect; priority one; promotion; radiation poisoning; replicator; Risa; sabotage; sector (unnamed); security officer; security team; sense of humor; shuttlebay doors; ; Solais V; Starfleet; Starfleet Command; Starfleet Security; tetryon; toast; tricorder; Tzenkethi; Tzenkethi autarch; Tzenkethi homeworld; Tzenkethi space; Tzenkethi warship; ; warp plasma conduit; "wide berth"; World Series;

Other references 
Deep Space 9 schematic: cargo turbo subsystem; crew quarters; crossover bridge; defense sail; defense systems monitor; deflector emitter; docking clamp; docking control cabin; docking pylon; docking ring; docking ring airlock; environmental purge/fill station; exhaust cone; fusion reactor assembly; habitat ring; ops module; ore processing center; phaser strip; photon torpedo launcher; power transfer conduit; promenade; radiator; reaction control thruster; runabout pad; sensor array; structural assembly; subspace antenna farm; tractor emitter; tug tractor emitter assembly

External links
 
 
 
 

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ru:Агрессор (эпизод)
Adversary, The