When the first “Alien” came out in 1979, promising and delivering screams in space that no one could hear, more than few critics and regular humans called it a relentless, hard-driving thrill machine. In retrospect it resembles a movie with the patience of Job, taking its sweet, stealthy time before arriving at one of the great moments in the history of extreme cinematic gore.

You know the scene, probably. There’s John Hurt, an actor whose face always seemed halfway to crestfallen even when he didn’t have anything to worry about, sitting around the spacecraft galley, having a jolly meal with his crew aboard the Nostromo. He doesn’t realize the steroidal tapeworm inside him, gestating, awaits the right moment to burst forth from Hurt’s chest and commence the cat-and-mouse franchise spanning two centuries and counting.

The new movie, “Alien: Covenant,” features Michael Fassbender times two and Katherine Waterston under coolly controlled duress.

It’s a maddeningly uneven picture, with an action climax staged and executed with the air of a contractual agreement. But as with “Prometheus,” the most elegantly wrought sequences make up for the monster stuff plainly less interesting to Scott.

A sleek, austere prologue finds weaselly Peter Weyland (Guy Pearce) enjoying his Mahler and activating his latest android (Fassbender), whom he names David, after the statue. The robo-lad’s head is filled with dreams of alien life forms and the glories of space exploration. Then, the movie proper: We’re aboard the Covenant, with a new, hapless crew of mortals. The year is 2104. This is a colonists’ ship, like the Mayflower, only with embryos and sleep-frozen humans.

Fassbender also plays android Walter, the latest-generation robot assisting the humans. Early on the spacecraft is hit by a neutrino shock wave, which takes the life of the captain (James Franco, in a hilariously brief cameo) and leaving the Covenant under the command of Capt. Oram (Billy Crudup, valiantly enlivening a role defined by insecurity).

The real star, though, is Waterston, the crew’s so-called terraforming expert and executive officer. She’s the can-do female lead evoking memories of Sigourney Weaver’s Ripley. The crew is headed to a faraway planet, but a mysterious radio transmission is too tantalizing to pass up. So it’s off to the planet where Prometheus met its doom.

Around the midpoint, “Alien: Convenant” takes a turn toward a “Planet of Dr. Moreau” storyline, stealing from H.G. Wells. Mostly, of course, the film steals from earlier “Alien” movies. Scott’s armful attempt to marry rousing bits from James Cameron’s “Aliens” (the “fun” one) with the brooding tone favored by Scott and David Fincher (“Alien 3”) has led to a product divided against itself. And yet I was consistently taken with Fassbender’s work, and with Waterston. I may be as conflicted about “Alien: Covenant” as Ridley Scott apparently was. But I’ll take it over “King Arthur.”

MOVIE REVIEW

“Alien: Covenant”

Grade: C+

Starring Michael Fassbender, Katherine Waterston and Billy Crudup. Directed by Ridley Scott.

Rated R for sci-fi violence, bloody images, language and some sexuality/nudity. Check listings for theaters. 2 hours, 3 minutes.

Bottom line: An uneven film that attempts to marry the original and sequels