In brief: Some anomalies, but reasonably engrossing and well acted overall.

Deep in the recesses of T'Pol's mind lies a dormant, repressed memory of a disturbing and volatile nature. T'Pol doesn't know it's there, but it's there nonetheless, and in the course of "The Seventh," it will grab her, shake her, and leave her reeling.

Seventeen years ago, she was an operative for the Vulcan Ministry of Security. She was specifically trained for an assignment to track down and capture seven Vulcan fugitives -- undercover agents who were accused of joining the corruption of a world government they were supposed to be investigating. (T'Pol remembers tracking only six of the seven fugitives, but therein lies the mysterious crux of the issue.) While on her mission, something happened, and the last of her targets, a surgically altered Vulcan named Menos (the always reliable Bruce Davison) escaped, never to be heard from again ... or rather, until 17 years later.

T'Pol receives a message from the Vulcan High Command telling her that Menos has been spotted on a remote world near Enterprise's current position, and that he's smuggling synthetic biotoxins that can be used for weapons. T'Pol is dispatched on a secret mission to finish the job she started 17 years ago. Only Archer and Mayweather, who accompany her in a shuttlepod, know the details of the mission. Trip is left in command of the Enterprise, which is idled in orbit of a planet elsewhere in the solar system.

"The Seventh" is clearly in the spirit of what on Voyager I called the "Borg psychological thriller." Those episodes -- "The Raven," "One," "Infinite Regress," "The Voyager Conspiracy" -- were about what happened as a result of a situation colliding head-on with the unique properties of Seven of Nine's Borgified brain. Those shows usually had Seven deeply troubled or going berserk over something that mainly existed in her mind. Now, with "The Seventh," we have a similar situation in T'Pol's head, a result of unique Vulcan mental disciplines inappropriately applied.

Jolene Blalock, whom I've criticized lately, turns in one of her best performances to date in "The Seventh." Blalock, I suspect, just doesn't have the "Vulcan thing" down to my satisfaction; something about it sometimes feels stilted and forced. I also suspect the writing for T'Pol often lacks a certain spark. But given an opportunity to show the cracks in her disciplined Vulcan control, Blalock -- and the writing for her character -- becomes much more engaging. You can put me in the camp that argues in favor of more emotional issues for T'Pol to deal with; I'm less interested in the monotone routine.

Coming off the heels of the puerile "Night in Sickbay" and boring test-pattern-like "Marauders," "The Seventh" is a pleasant relief that returns to the characters and tells a good, solid story. Menos, when we encounter him, is a character we respond to: We're not sure whether he's telling the truth or inventing self-serving lies, but we're involved either way. He says he's not a smuggler as the Vulcan government claims, but merely a target of a probe that wants all their former agents recalled at any cost. Bruce Davison is a perfect choice for this sort of role, because he's an actor who is equally believable as an innocent victim or a play-acting villain. He effectively wins our sympathy even as we're wondering how much of Menos' story is fabricated.

Going head-to-head with Menos is T'Pol, whose repressed memory is a ticking time bomb to an emotional meltdown. Without overreaching, Blalock is able to suggest a percolating emotional volatility beneath the surface that T'Pol is trying with all her might to suppress, with little success. She regards Menos with an icy glare of contempt that Blalock excels in selling, and as her repressed memory creeps its way into her conscious mind, T'Pol seems vulnerable and on the verge of a breakdown. The performance is right on the mark, and I believed it.

The repressed memory involves another of T'Pol's mission targets, Menos' partner Jossen, whom she killed when he drew a weapon on her. Unable to cope with having taken a life, T'Pol underwent an obsolete Vulcan mental ritual to repress the memory of the killing along with her emotions of it. Tracking Menos now has brought the repressed memory back to her consciousness. The episode uses briefly inserted flashback images -- jarring and visually effective -- to hint at and ultimately play out for the audience the 17-year-old incident involving Jossen's death.

Menos, observant and opportunistic, tries to use T'Pol's obviously emerging weakness to his advantage, playing upon her guilt. He paints Jossen as an innocent wrongly accused by the Vulcans and dead at T'Pol's hands because of it. Menos pleads his case by saying he doesn't want to be doomed to walk the same path. Some initial evidence suggests that perhaps Menos is even telling the truth, which sends T'Pol into a whirlpool of self-doubt involving her past and present actions. But as Archer notes, the Vulcans sent T'Pol on this mission to capture Menos, not determine his guilt or innocence.

I liked the dynamic between Archer and T'Pol; it's right where it should be -- featuring a bond of growing trust, respect, and friendship between the captain and first officer. When T'Pol is thrown into chaos by the psychological turmoil, Archer is there to help guide her in the right direction. Indeed, it's a downright shame that "A Night in Sickbay" had to play moronic games involving "sexual tension" and hint at a romantic subtext, because I found myself waiting here for the other shoe to drop. Thankfully, it never does; such subtexts are nowhere to be seen. Sanity has apparently prevailed.

As a production, there's plenty to recommend in "The Seventh." The station where all this takes place -- essentially a truck stop for starships -- is set on a snowy alien world that provides some appealing visual flair. The station's tavern has a wooden motif that gives the episode a sort of Western-wilderness atmosphere that is refreshingly non-Trek. I also liked the fiery action sequence when Menos sets the tavern ablaze.

Of course, there are some details I found a little bit perplexing, like the whole need for all the Vulcan cloak-and-dagger secrecy. T'Pol brings Archer and Mayweather into this plot reluctantly, while the rest of the crew is left completely in the dark. This is presumably because the Vulcans don't want to broadcast their role in infiltrating off-world government corruption, but I didn't quite understand why Archer couldn't give Trip so much as a hint about this mission since, as Trip points out, details would be useful in the event of an emergency.

Also, showing Trip in command proves to be a bit of a mixed bag. It's played for some light, understated comedy that's fairly amiable, but from what we're shown, Trip is indecisive to a fault, forever telling people, "I'll get back to you." It doesn't speak well for his leadership abilities that he can't give anyone a straight answer so they can do their jobs. Considering he's in command of engineering and third-in-command on the ship, I find it a little hard to swallow that this is how he would actually approach command, whether the ship is in an idle situation or not.

And then, of course, I must again point out this series' tendency to treat Mayweather as a cipher, even when he's in the middle of the story's action. Archer orders him around with little in terms of respect (such lines as "Get back over there" and "Go back to the cockpit, Travis" are delivered surprisingly coldly). Also, many scenes are shot as if consciously trying to minimize Mayweather's presence in the frame, as if he's not worth the camera's attention. It's downright odd. What gives?

I also wonder about the notion of the trained Vulcan elite in the Ministry of Security who are yet somehow unable to cope with the prospect they may have to take a life in the course of their duty. (And if it's such a problem, why didn't T'Pol use the stun setting when firing on Jossen? After all, she uses the stun setting to capture Menos here.)

Despite these qualms, I liked the net result. As a show where T'Pol is going up against her own psychological terror as well as Menos' scheming, "The Seventh" gets the job done. A final scene suggests that T'Pol will be deeply affected by reacquiring the repressed memories; she looks as if she's just been whacked with a sledgehammer. Blalock shows that she may be more interesting to watch when playing a character facing internal conflict in regard to her emotions than one who has everything under precise, Vulcan-like control.

Given that, I certainly wouldn't mind seeing the troubled side of our resident Vulcan surfacing more often.

Next week: Our newest Trekkian cast does their rendition of "A Piece of the Action."

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Next episode: The Communicator