Nutshell: Extremely impressive. Startling, exciting revelations, and some major character highlights. One of the series' best.

Read no further unless you have either seen "In Purgatory's Shadow" or you absolutely don't care about being spoiled, because the surprises in this episode are part of what makes it so fascinating, and I will be revealing those surprises. With that said, I'll continue.

"In Purgatory's Shadow" is a huge, encompassing episode on the Dominion front of Deep Space Nine. It's also a stellar little Garak show. The overall package is yet another hour of DS9 that I would easily put up there with the very best.

In many ways, this installment feels like the long-deferred follow-up to the "Improbable Cause"/"The Die is Cast" thread from season three. It succeeds for many of the reasons that stellar two-parter did. While "Purgatory" isn't quite as convoluted in its plot workings as "Improbable" was, what happens in the course of the hour is easily as startling and compelling, and as the events unfold to the ultimate "To be continued" sign, we wonder how in the world they will wrap it up, and must patiently wait a week to find out.

In the meantime, we've easily got ourselves the most purely substantial and consequential episode since "Rapture," the best Dominion story since "Homefront," and the most interesting Garak-oriented plot line since "Improbable"/"Die."

As the episode begins, the DS9 crew receives a coded Cardassian message from the Gamma Quadrant. Garak is able to quickly decode it, discovering that it's from his mentor Enabran Tain, the former-head of the Obsidian Order presumed dead after his battle with the Jem'Hadar in "The Die is Cast."

This is the first of many surprises. I never expected to see Tain again after his ship exploded in "Die," but now that I think about it, it's certainly possible that Tain would've had an escape plan if he's as clever as the creators have always drawn him. I always found Tain interesting, and it was definitely nice to see this character again, as well as the revelations he has in store (more on that in a moment).

From here the plot quickly begins developing, unfolding into a huge canvas. At the same time, Behr and Wolfe's script offers a variety of interesting little character pieces. The way the smaller characterizations balance against the taut, important plot is stellar.

Opening the show, for example, is a quiet scene between Kira and Odo discussing his refound shapeshifting skills. It's sensible because it knows just how much time to devote to itself. The whole scene takes no more than a minute, yet it proves the writers haven't forgotten about the issue. The same goes for a later scene between Kira and Dax about the O'Briens' new baby.

And there's more. There's some winning character interplay involving the convoluted relationships between Dukat, his daughter Ziyal, Garak, and Kira. I won't go too far into detail on this matter, but the piss and vinegar between Dukat and Garak is welcome; the complex scenes between Dukat and Ziyal are interesting; Dukat's blaming of Kira for allowing Ziyal to pursue a friendship with Garak is an eye-opener (and Kira's reaction to Dukat's attacks further drives home the much-appreciated notion of the "real" Kira being back). Heck, even the scene between Worf and Dax works fairly well (much more than can be said of the last time we saw their relationship explored in "Let He Who Is Without Sin...", that is)--although I still think Worf looks too utterly confused whenever Dax is concerned.

The story's use of these character points is wonderfully handled. They aren't directly related to the plot in all circumstances, but they never detract from what's going on. On the contrary; they add to the overall texture of the episode.

Still, plot is a key element featured in "Purgatory," and there's a lot of it. I, for one, have been awaiting a major Dominion payoff that would dare to break from the status quo for some time now, and with the end of "Purgatory," it's certainly imminent.

The plot progresses as Worf and Garak venture into the Gamma Quadrant to track down Enabran Tain's signal. En route there's a wonderfully amusing Garak scene as he practices his lying skills on Worf. Garak's dialog is about as sharp as I've heard it (perhaps since the aforementioned "Improbable," which was the dialog show of all dialog shows). The way he talks of joining Starfleet seemed so initially sincere that even I thought he meant it. (You've gotta love this guy.)

To avoid Jem'Hadar surprises, Garak and Worf pilot the Runabout into a nebula... only to find a hidden Jem'Hadar fleet already hiding there. It has to be a prelude to an invasion, Worf realizes. Why else would the Dominion hide such a large fleet so close to the wormhole? The Jem'Hadar tractor and board the Runabout, but not before Worf sends out a signal warning the station.

Worf and Garak are taken to a Dominion prison located on an asteroid. It's here where some exciting revelations come flying at us like hardballs.

This prison (where a prisoner's crime is merely being an "enemy of the Dominion") seems to also be a place where the Dominion relocate those who have been mysteriously replaced by Changelings. Within minutes of their arrival, Worf and Garak find General Martok (J.G. Hertzler)--the Klingon replaced by a Changeling infiltrator two years ago and exposed in "Apocalypse Rising"--among the prisoners. (The Jem'Hadar, by the way, always enjoy fighting Klingons in their spare time).

Martok's presence is one of many very nice and intelligent touches to the story. It builds upon past stories (like "Apocalypse Rising" and "Way of the Warrior") and brings new realizations to the surface. For example, one disturbing point that comes to mind is that the blood screenings Starfleet uses to detect Changelings may very well be useless. If Martok was replaced two years ago, it would've presumably been before "Way of the Warrior"--in which case the Martok who performed his own blood screening in that episode to "prove" he was the genuine article was really, in fact, a very clever shapeshifter.

Perhaps the biggest plot surprise is dear Doctor Bashir. You see, Bashir turns out to be in this prison--because he himself has been replaced by a shapeshifter. The Bashir on the station is a Changeling spy who has been there for, as Bashir says, over a month. Judging by Bashir's uniform and the time indications he explains ("I went to bed one night and woke up here"), I'm guessing that he was replaced sometime between "The Ascent" and "Rapture." Upon this revelation I was sincerely shocked. It's a brave move on the writers' part (though I hesitate to think that all the nice renditions of Bashir in "Rapture" were Changeling imitations)--if there's one way to get the audience so viscerally involved in a subversive, convoluted Dominion plot, this is it.

Then, of course, there's Enabran Tain--who has been prisoner on this asteroid ever since "Die is Cast." His being alive was surprise enough, but there's a bigger payoff here that goes beyond Changeling trickery and imminent invasions--and it explains so much about Garak and Tain's relationship that one might say it explains everything. Tain is dying in this prison, and before he dies, Garak has just one request: that Enabran acknowledge him as the son he is. Tain resists, almost instinctively. Garak, being the son of the head of the Obsidian Order, has always been Tain's own Achilles heel, and based on what we know of Garak, Tain, and the Obsidian Order, it makes absolutely perfect sense that Tain would exile his son from Cardassia, to protect a "bigger picture." It's tragic, yes; but absolutely wonderfully realized, and Tain's deathbed scene with Garak is played so right that I can't imagine that the situation could've turned out any other way. Andrew Robinson, as usual, is stellar; when Tain slips away his reaction is so subtle, yet so revealing in a "Garak" kind of way. The scene is moving and so nicely done that it earns four stars for the episode all by itself. And the way Gabrielle Beaumont directs this scene and then presses on with plot right afterwards is superb. High, high praise is deserved all around.

As standout as this moment is, I don't want to take away from the rest of the story, because it as well is excellent. While Garak, Worf, Bashir, and Martok are dealing with their problem in the prison, Sisko and the crew prepare Deep Space Nine (with the little time they have) for the imminent Dominion invasion. This side of the story is also consistently compelling. There are many nice little moments that make the station's situation seem genuinely urgent and fearfully real. Everything--from Kira's short Defiant scout on the other side of the wormhole to see what's brewing ("Trouble," she says ominously); to Sisko's announcement that the recent Borg attack and war with the Klingons has left Starfleet "spread pretty thin" and susceptible to an invasion; to Kira's concern that the solution of sealing the wormhole to prevent an invasion would leave Bajor disconnected from the Celestial Temple; to the fact that Bashir is really a Changeling roaming the station ready to unleash an entourage of sabotage--everything here is relevant and fascinating.

"In Purgatory's Shadow" works on just about every level I can imagine. The characterizations are flawless, as far as I can tell; the plot is riveting; the revelations are surprising; the acting, directing, special effects, photography are all top-notch; and I was pretty much absorbed from beginning to end.

Right down to the moment the crew's attempt to seal the wormhole failed and the swarm of Jem'Hadar ships came streaming out of the wormhole.

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Next episode: By Inferno's Light