More foreboding is the result of DS9's season three finale, a "quasi-cliffhanger" like "The Jem'Hadar" that's a punchy adventure story in itself while also promising that it's just one of many more to come in the Dominion saga. Here the Dominion affirms itself as a dangerous, malevolent enemy that will be knocking on the Federation's door next year, if not pounding it down. They truly hold the intimidating creepiness that the Borg had looming over TNG after "Q Who."

But first, the lighter moments.

The show begins with a long-awaited character moment as Sisko is awarded his promotion from Commander to Captain. I knew it would happen eventually, but happening in this episode proves to be one of the season's most unexpected and pleasant surprises. Finally, Sisko can say "Captain's Log." I like it.

Another character element I like is the continued back-burner development of the Sisko and Kasidy Yates relationship. Since the creation of Captain Yates' character in "Explorers," the writers have done exactly what should be done with relationship stories on Star Trek: They're taking the slow, subtle, plausible route--keeping it alive while not going overboard. In this outing, Dax presses Sisko for some information about their relationship. The results are, in a word, amiable. Indeed, the writers have worked with Sisko a lot this season, and the results have been very good.

From here, "Adversary" delves into a Defiant-based plot when Ambassador Krajensky (Lawrence Pressman, who also guest-starred in "Second Skin") orders Sisko to take the Defiant on a one-week patrol of the Tzenkethi border. The Federation had been at war with the Tzenkethi over a decade ago, and Krajensky brings news of a coup on their homeworld which could potentially be the beginning of another Federation threat.

Upon leaving the station, O'Brien and Dax discover the Defiant's command systems have been sabotaged. Radiation residue places Ambassador Krajensky at the scene of the crime, but the crew discovers Krajensky is not who he appears to be when he suddenly morphs into an air vent and escapes. Krajensky is a Changeling.

The Changeling's sabotage devices allow him to take control of the ship, which he pilots straight for Tzenkethi space with all weapons armed. He hopes to start a war between the Federation and Tzenkethi by hitting the Tzenkethi fast and hard. With the Federation busy fighting the Tzenkethi, the Dominion would presumably have little trouble coming through the wormhole and conquering the Alpha Quadrant.

Obviously, the crew must stop the Changeling at all costs. Sisko sets up teams of two, armed with phaser rifles to systematically search the ship for the Changeling. Making the task difficult, however, is the fact that the Changeling can look like anything--or anybody.

And here's where "Adversary" works best. It's the best-case scenario for a Star Trek plot along the lines of The Thing. It becomes quite an effective paranoid thriller--working the gears where Voyager's "Cathexis" failed miserably.

Unlike that outing, this episode proves genuinely intense in many places, with its healthy doses of crew paranoia and creepy Changeling masquerading. There's even a blood test Bashir performs to determine if one of the crew members is not as he appears (brrrr...). For most of the way, director Alexander Singer paces the suspense quite well through an impressive collection of Defiant sets, and he gets the helping hand from a fairly effective Chattaway score.

There are also some good character moments, such as the scene between Sisko and Lt. Commander Eddington (Kenneth Marshall) when they discuss the personal meanings of rank. Eddington also has some good scenes with Odo. One reveals the fact that throughout his years as security chief, Odo has never fired a weapon or taken a life, and he doesn't intend to start now with one of his own kind. Very interesting stuff.

Even the seemingly obligatory idea of Sisko arming the Defiant's auto-destruct sequence makes sense here. (Although, is it too much to ask why the auto-destruct program was not disabled by the Changeling's devices?) "One thing is for sure," Sisko says. "We're not going to start a war with the Tzenkethi." This gives Chief O'Brien a limited time to regain control of the ship. Meanwhile, Odo chases the other shapeshifter through the air vents.

One thing Alexander Singer severely botches is the timing on the computer's destruct sequence warnings. A glaring 2 1/2 minutes vanish into thin air when the auto-destruct countdown jumps from ten minutes to seven minutes in an interval of less than 30 seconds--way too noticeable to be ignored. (At the very least, he could've cut briefly to an external view of the ship to signify time passing.)

Something the writers severely botch, however, is Sisko's behavior after he arms the auto-destruct. As the fate of the ship lies in O'Brien's hands, Sisko displays a helplessness that borders on downright apathy. This is completely out of character and I don't like it. I know Sisko better than that!

And of course, you know the writers had to throw in the two Odos trick, presented here to O'Brien in the engine room as he attempts to disable the Changeling's ship takeover devices. Fortunately, this overused bright idea is satirized when O'Brien unleashes the season's best-delivered one-liner--"Look, I have more important things to do than play 'Choose the Changeling.'"

The final showdown plays out here between Odo and the Changeling, ending when the evil shapeshifter is fried by warp core radiation during their struggle. The sequence boasts some impressive CGI morphing effects but, more importantly, gives Odo a personal tragedy when he's forced to take a life for the first time--while also being the first to break the tradition "No Changeling has ever harmed another" by killing one of his own kind. Although this ending is a bit abrupt and Lawrence Pressman doesn't get much in terms of interesting dialogue with Odo, his death scene of reverting into a liquid and then crumbling into dust is a well-realized visual effect. The Changeling has a final message before dying. "It's too late," he whispers to Odo. "We're everywhere."

The idea of a threat from within is still fascinating--reminiscent of the never-developed TNG plotline "Conspiracy." Also, the Dominion has fully established itself in the Trek encyclopedia of villains this season, and we will surely see them again. However, "Adversary" brings up some concerns about what the intentions of this storyline are. In one year, the Founders have gone from Gamma Quadrant monitors to Alpha Quadrant spies. If Dominion operatives are "everywhere," where does DS9 as a series lie?

On one hand, it's nice to know the Defiant is available to escape the station for a fresh starship story. On the other hand, I worry that the writers may forget about Bajor's problems in favor of feeling compelled to go the TNG action/adventure route. And by having the Dominion infiltrate the Federation, they may be over their heads in internal conspiracy--something the series has no real obligation to stress considering the station is on the very edge of Federation space. Bajor has its own problems to deal with. Do we really need to have an attack on the heart of the Federation?

For that matter, is the Defiant really the ship that should be sent on a Starfleet mission like this? (Episodes like this always make me wonder who's left in charge of the station.) One Defiant issue that never really got resolved was what happened to the severe flaws the ship had. Unless Sisko has become an extreme risk-taker by ordering maximum warp of a ship which should tear itself apart at such speeds, we have to assume these flaws were fixed. Still, it would've been nice to at least have a line explaining it.

In any case, "Adversary" is a good season finale--entertaining, suspenseful, and a lure for viewers to come back next season. As for what the writers plan to do with this most extreme threat, only time will tell.

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Next episode: The Way of the Warrior

End-of-season article: Third Season Recap