Fox' record $80 million payment for TV rights to the second-rate movie sequel produced a whisker-thin first-place finish among its target viewers, ages 18 to 49 — for one week. To achieve even that marginal distinction, the film needed help from the prime-time spillover of a hot NFL game. By big-event standards, "Lost World" ratings were decidedly mediocre — on the first of the 10 runs Fox purchased.

Fox' Sunday-night fate rests not in the wildly overpriced claws of computer- generated dinosaurs but in the tangled web of conspiracies, coverups, monsters, aliens and genetic engineering of "The X-Files."

And that fate — with the phenomenal series poised at the start of its sixth season — is far from certain.

Indeed, Fox is playing a very high-stakes game with this essential element of its prime-time schedule:

Last summer's feature-film spin-off, "The X-Files: Fight the Future," did decent box-office business, but it also proved creatively disappointing (or worse) to legions of committed fans of the TV show, including me.

Although connections are hard to pin down, the film's shortcomings, if not its mere release, surely had something to do with the depressed ratings for "X- Files" reruns on Fox over the summer.

The movie also failed in another of its key missions: to help intensify and broaden the excitement about and anticipation of the series' return this fall with fresh episodes. If there's a lot of buzz about Sunday's season premiere, I haven't heard it.

That's too bad; it's a terrific episode on most counts. The opening "previously on . . ." recap, for example, ingeniously includes elements from both last season's cliff-hanger and the feature film.

The new footage begins with a classic "X-Files" device: pseudo-normalcy. A carful of seemingly normal, carpooling co-workers is headed home at the end of the day. Well, all but one of them seems normal.

Distinctly abnormal (i.e., gruesome) events happen immediately, eventually drawing in Agent Mulder (David Duchovny) and Agent Scully (Gillian Anderson). Among the featured characters returning from last season's concluding episode are Agent Diana Fowley (Mimi Rogers) and that smug liar Agent Spender (Chris Owens).

The episode, written by series creator Chris Carter and directed by Kim Manners, deftly weaves together what feels like dozens of dangling plot threads into a whole that, if not entirely comprehensible, is thoroughly engaging. Carter also has included several impish gibes — some subtle, some not so — that take aim at a variety of targets, including the show itself, the feature film and some of the film's critics. And you might want to take special note of the name of a worker at a nuclear power plant.

But the upcoming "X-Files" landscape is not entirely sunny. An avowed homage to "The Wizard of Oz" written and directed by Carter — titled "Triangle" and scheduled to air Nov. 22 — attempts to blend time travel, parallel universes, Nazis and the Bermuda Triangle but turns out to be a chaotic, inconsistent mess.

If not for the novelty of its letterbox presentation (wide picture, black borders top and bottom) and some exciting camera work, the episode would qualify as one of the series' rare best-not-seen installments.

Looks like we're in for a bumpy season, Toto.