Brendan Fraser as Gunther and Dominic West as Noah in "The Affair." (Phil Caruso/ Showtime)

One small problem with the very best TV shows is that they have to keep going forward. That’s what TV shows do — unlike, say, great films that remain forever fixed at the place and time and mood in which you left them, protected from tampering instincts or an obligation to push on. To stay on the air (and in the air, buzz-wise), a good TV drama has to keep paving new twists and turns on a road that eventually leads to a satisfying destination. This can also be the same dangerous road on which wheels have a way of flying off.

All of which is my way of saying that the first few heavily burdened episodes of the third season of Showtime’s sharply satisfying drama “The Affair” leave me a bit ambivalent about the idea of moving along. (Stop reading here if Seasons 1 and 2 are still lingering on your to-watch list; this review will discuss the story so far, with a taste of what’s to come.)

Last season, I was busy admiring “The Affair’s” complicated structure and philosophical approach to the nature of truth, in which four (or more) characters experience notably different versions of the same emotional cataclysms. My enchantment left me ill-prepared for one of the show’s least satisfying swerves, in which an objective and omniscient point-of-view stepped in and resolved a mystery: On trial for murder, the self-absorbed Noah Solloway (Dominic West) shocked the courtroom by confessing that he drove the vehicle that killed slime bucket Scotty Lockhart (Colin Donnell), ex-brother-in-law of Noah’s new wife, Alison Lockhart (Ruth Wilson).

Rather abruptly, a show that firmly believes that no two people can see something the same way made one mutual secret quite plain to viewers: Noah was not driving the car that night; his ex-wife, Helen (Maura Tierney), was driving, but Noah took the blame for it and was sentenced to prison.

Season 3 takes a considerable leap forward in time — a year or two at least — and starts with an entire hour devoted to the perspective of Noah, the show’s least-reliable viewpoint. Freshly paroled, Noah is teaching creative writing at a New Jersey college while nobly struggling with everything he has lost, including his relationship with Alison, his marriage to Helen, the respect of his children and the fleeting success of his semi-autobiographical novel that bared too much. (Everything Noah does is tinged with conspicuous nobility and literary manliness; he’s an author caught up in his own world.) To top it off, he’s being harassed by a menacing guard (Brendan Fraser) who has taken a grudge beyond the prison walls.

Although “The Affair” remains one of the most interesting and well-written dramas around, West’s portrayal of Noah has outworn some of its welcome; he’s far more interesting when his libido takes precedence over his angst. As the story continues to sprawl, “The Affair” loses sight of its main draw — a torrid extramarital affair between Noah and Alison, the singularly bad decision from which so many more bad decisions have flowed.

Alison has moved on; by Episode 2 we see that her primary goal is to return to Long Island and win partial custody of Joanie, the daughter that Noah believed was his child and who is now living with Alison’s ex-husband, Cole Lockhart (Joshua Jackson), the child’s true father.

Typing this up feels like I’ve been reassigned to telenovela recaps. It’s better to simply note that “The Affair” succeeds by becoming a tangled mess — but that mess has considerably less appeal this time.

The only way through, of course, depends on Tierney’s unerring performance as Helen, Noah’s ex, whose first-world suffering is an exquisite balance of permanent guilt and self-interest. Jackson, too, as Cole, often comes to the rescue with an alternate story line, although he is seldom seen in the episodes made available for review. I don’t suppose there’s any way we can get Helen and Cole together, and reignite “The Affair” in a properly heated fashion?

The Affair (one hour) returns Sunday at 10 p.m. on Showtime.