For its first 30 or so years of existence, the Alien series, whatever its ups or downs, was a model of franchise-by-auteur. By most accounts, this was an accident of behind-the-scenes growing pains as much as a creative ethos. But it was an accident that resulted in each entry being made by a different and distinct filmmaker: Ridley Scott, James Cameron, David Fincher, and Jean-Pierre Jeunet made four vastly different movies out of similar material. Even a disreputable cash-grab crossover movie during a low ebb for the series, Alien vs. Predator, is very much the product of its B-movie maestro, Paul W.S. Anderson.

But in 2012, Ridley Scott, director of the 1979 original, returned to the series. Scott's hotly anticipated Prometheus was a prequel to Alien; it didn't exactly feature the iconic multi-mouthed creature designed by H.R. Giger, but explored the origins of early forms of that creature. Now Scott and the creature have returned for Alien: Covenant, part sequel (to Prometheus) and part prequel (to Alien, again).

It's a strange and surprising direction for the series, even as it conforms to modern Hollywood rules that even well-respected A-list directors should engage in franchise maintenance. Scott has one of the more eclectic resumes in mainstream cinema, with hits as diverse as Thelma & Louise, Gladiator, Hannibal, Black Hawk Down, The Martian, and American Gangster, as well as his groundbreaking Blade Runner. For decades, he never revisited his own material. Now he's made two Alien prequels and plans to make at least one more.

So why is Ridley Scott suddenly in the Alien business again?

It's a knotty question in part because Scott's eclecticism disguises what amounts to a journeyman's career. His films are polished, well-assembled, stylish, and a little bit more anonymous than his reputation suggests. A close look at his filmography does reveal certain thematic commonalities — he likes to see characters fight or puzzle their way out of extreme circumstances, and often shows an interest in unfussy professionalism — but Alien is so great that it dwarfs a lot of his other work. There isn't much to chew on in the slick entertainment of The Martian.

But it's nearly impossible to make an Alien movie without subtext, and in Alien: Covenant, Scott runs with the opportunity so eagerly he sometimes forgets the "sub" part. In the opening sequence, a prequel to the events of Prometheus, a wealthy industrialist (Guy Pearce) chats with his android creation David (Michael Fassbender). If you created me, David wants to know, then who created you? "It's a question for the ages," Pearce then has to say, out loud.

Scott obviously agrees. Prometheus followed David and some human scientists on a mission to discover their deep-space origins. Covenant initially picks up with a different spaceship crew, complete with Walter, their own android — also played by Fassbender, but in an exaggerated flattened-out semi-American accent to emphasize his compliance, as contrasted with David's haughtier, more mischievous English tones. The crew is leading a colonization mission to a planet that may be hospitable to human life, but get woken up from cryo-sleep early by a ship malfunction. They also pick up a signal from another, much closer planet, that the captain (Billy Crudup) thinks may be an even better environment for their new beginning.

It's difficult to say more about the plot of Covenant without spoiling it, especially because it's structured as a mystery — not to the characters so much as to the nerds in the audience, wondering how or if this can tie into the events of Prometheus. Suffice to say that the crew does encounter our old friend David, and his tinkering with alien life forms seen in the previous movie has continued offscreen. His creations are moving toward that perfect killing machine first seen in Alien. In Prometheus, they looked like distant cousins. In Covenant, they look like close siblings.

Fassbender's double role is one of the best non-technical things about Covenant, which like its predecessor is gorgeously shot and designed, with some truly stunning spaceship interiors and futuristic pointillist holograms. Scott sometimes resorts to boilerplate visual tricks like toying with frame rates, and there's some of that during the movie's action bits. But he also ups his game in quieter scenes, like one where David tries to teach Walter how to play music on a pipe. It's an eerie Fassbender-on-Fassbender sort-of seduction where the camera keeps drifting between the two of them, floating with delicious tension as they size each other up.

The fully human characters, though, are even sketchier than last time. Katherine Waterston plays a sort of proto-Ripley, but doesn't have the natural grit of Sigourney Weaver — not that the movie gives her much chance to show it, anyway. Danny McBride avoids comic-relief shtick and is a welcome presence on the crew. Many of the rest (including a cameoing James Franco) are far more interchangeable than the near-identical Fassbender characters, and often treated as cannon fodder. Scott asks questions about humanity while appearing less interested in it than ever; his heart clearly belongs to the scheming androids and vicious aliens.

That's not necessarily a bad thing. Maybe Scott identifies with David, even at his most wicked, because his actions mirror Scott's strategy with these Alien prequels: The filmmaker is also tinkering, adjusting different ingredients (mourning but strong woman; seemingly subservient but possibly nefarious robot; Alien-like aliens) until, presumably, the series arrives at the moments before the first film. He's opening up his original creation and seeing what makes it tick.

And so Covenant is far less smooth than the elemental simplicity of the original film, so often described as a haunted house in space. It's kind of a retread of Alien, kind of a continuation of Prometheus, and kind of a mad scientist/monster movie with the order of operations scrambled. Some of it is genuinely bonkers, and some of it is just more stalking and goring.

That scrambled, searching quality makes Covenant both oddly satisfying and satisfyingly odd, even if many of its plot turns are predictable and its non-Fassbender characters negligible (they seem designed to disappear before the next iteration, just as few Prometheus cast members made it to this movie). It feels more revealing than the typical Scott movie, and it reveals a deep skepticism of the very process of creation, especially of creating life. There's reproductive unease at the core of many Alien movies, but Scott's prequels turn the very thought of creating anything in one's own image or whims as a doomed proposition.

This is both the strength and the peculiar weakness of Alien: Covenant. It feels very much a product of Ridley Scott — and even helps clarify what that even means. Yet more than the original quartet of Alien pictures, it's to some degree about itself — an Alien movie about the perversity of making Alien movies. It also, in conjunction with the underrated Prometheus and the as-yet-unmade sequel, feels drawn out. Though his Alien prequels rank among his best mid-to-late period films, they make you understand why so many other filmmakers were ready to cut and run.