Skylines — the third installment of a sci-fi action trilogy whose creation spans the last decade and was made on a relatively small budget — breaks barriers when it comes to writing sci-fi with heavy special effects for the big screen, and also bends a few trilogy story conventions as well.

Skylines takes place in the aftermath of a post-alien invasion Earth now shared by humans and alien-human hybrids. The hybrids, created when their human brains were forcibly transferred to alien bodies, are being infected by a rapidly spreading virus and starting to turn on their human counterparts. Captain Rose Corley (played by Lindsey Morgan) — herself a unique being born of a human mother infected with alien DNA — leads a team of soldiers to the alien homeworld to bring back a device powerful enough to stop the virus and save the hybrids. 

It’s Aliens meets Starship Troopers meets Independence Day — but pulled off by writer-director Liam O'Donnell for a fraction of their budgets even with high-level effects. Sci-fi screenwriters dissuaded from writing epic films with big-graphics budgets can take heart from his success story.

O'Donnell began this journey by writing treatments for commercial projects and music videos for Greg and Colin Strause, then moved on to working on their pitch for Aliens vs. Predator: Requiem with them. His “film school” was getting involved as an on-set consultant planning action sequences with his then-roommate who was their concept artist once they’d landed the film. 

He was also working on developing his own scripts, including a couple of more epic sci-fi and fantasy ideas but eventually landed on Skyline, the first film of the three-part franchise, which he co-wrote with Joshua Cordes and was directed by The Brothers Strause, with an overall budget of about $10 million. Most of the budget apparently went straight to the special effects they used to generate the impressive invading aliens and their ships.

They accomplished this by keeping their live shooting primarily contained to one location, mostly in Greg Strause’s new penthouse apartment in Los Angeles, as well as the rooftop, garage, pool deck, hallways, stairs, and grounds. O'Donnell and Strause both lived in the same building and were able to negotiate an excellent deal with the homeowner’s association and were able to finish all the shooting in about a month. The film grossed just under $67 million overall, and O'Donnell remains grateful for their luck at landing a worldwide release in 2010. 

Though described as a sci-fi action thriller, Skyline turns the tables on the genre and functions more like a horror film with a cast of ordinary innocents struggling to survive a shocking and wholly unexpected alien invasion, especially as they get picked off one by one, rather than epic heroes taking down the invaders. 

Beyond Skyline, the second installment made in 2017 — which carries little of the original cast over from the first movie — was made for about $14 million, written and directed by O’Donnell himself and shot in part in Indonesia. O’Donnell chalks up the change in cast to practical matters of talent availability but the Skylines trilogy does something fascinating: it models the concept of playing with different stories set in the same world circumstances, rather than with the same characters. Part of why this seems to work are the teasers at the end of each film for the next one, including one at the end of this new release. 

Beyond Skyline, filmed for a comparable budget, goes farther with more elaborate sets and locations; O’Donnell ruefully says his attachment to specific locations and switches (set pieces moving characters from one location to another and requiring their own complex sets) drove his budget up a little higher. His experience with Beyond Skyline taught him to be less stubborn and less attached to his locations and more flexible and resourceful as he moved into making the third film. He says, “the experience and the practicalities of filming just make you a better writer and make you a more flexible writer.”

Skylines (stylized as Skylin3s) — the newest installment — was shot for close to the same budget as the other two, within a million or two of either one. O'Donnell got good and creative with this installment too, rewriting his script to take place in London instead of L.A. when they were offered a U.K. co-production opportunity, and making the most of reusing his sets to keep costs down. 

Story-wise, budget constraints and creativity aside, this time O'Donnell went full-out for an epic sci-fi story more along the lines of Aliens and Starship Troopers. Though he began the trilogy with ordinary people in an extraordinary world, he’s leveled up in this tale to focus on an extraordinary, super-powered female captain fighting for the survival of the human race. 

In this, Skylines breaks the “rules” of a trilogy. It’s not about an ordinary character from a first film returning and defeating the villains in the end à la Star Wars. No, there’s an almost wholly different cast in each film, handing off the tale like they’re passing a baton, each episode raising the bar on what’s possible in terms of cast, location, and story breadth. It’s unusual and creative, and seems to work inside this brand O'Donnell has built up over this last “bizarre decade” of his life. 

O'Donnell’s advice to sci-fi screenwriters looking to break in? Go for something along the lines of his first film, with “everyday characters, because it has that basis in our real world with a twist” and “will still have the easiest sell,” while “farther in, the more genre is demanded and at the highest budget level.” In other words, aim small to start, make smart budget choices, and get in there and make it yourself if you can. To do this, “…find an awesome cinematic location and make a story around it. If you're struggling in any way, sometimes basing things off reality and as practically as possible will unlock you.”

What’s next for O'Donnell? He’s attached to direct a post-apocalyptic martial arts epic, The Last Savage, which he co-wrote with executive producer Derek Kolstad, writer of the John Wick trilogy, whom he says “‘de-nerded’ his sci-fi stuff” and gave the characters more room to breathe.” He describes it as a futuristic, Gladiator-type of movie in new fighting arenas, taking place in Asia after a worldwide cataclysm. “Again, all easy-to-shoot, low-budget stuff.”

Will there be a fourth episode of the Skylines franchise? “Well, movie gods willing, I try not to count any chickens before they hatch,” O'Donnell says, “but I think we're kind of strangely just hitting our stride.”

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Skylines releases on Dec. 18 through Vertical Entertainment in select theaters, drive-ins, on-demand and digital.

Watch the trailer for Skylines here.