Lou Harry’s more than 40 books include Creative Block (Running Press), The Encyclopedia of Guilty Pleasures (Quirk Books), and the novelization of Santa Claus Conquers the Martians. His produced plays include Midwestern Hemisphere,The Pied Piper of Hoboken and Popular Monsters.

Just about every movie requires a leap of faith of some degree or another.

Trust us, says the biopic: None of us were there when this event actually happened to these people we never met, but we’re going to show you what they said and did anyway and expect you to buy it as fact.

Trust us, says the musical: Nobody you know may break out into an original song when emotions get high, but these folks do. And there’s an orchestra tucked away somewhere about whom you aren’t supposed to ask any questions.

Trust us, says the action adventure: The most athletic person you know may get winded after running a few miles, but a50-plus-year-old Tom Cruise can have a knockdown-drag-out fight and still leap onto a helicopter and climb a cliff or two.

Some films, however, require a larger leap of faith than others, which brings me to Mortal Engines.

This new science-fiction adventure asks viewers to believe that — a thousand or so years after an apocalyptic event pretty much wiped out mankind and destroyed most technologies — mankind has figured out a way to construct mobile cities, the largest of which are able to chase down and gobble up smaller ones.

Imagine Indianapolis heading northeast to eat Muncie. Now imagine Muncie folding up its Ball State buildings like a Transformer and booking it up I-69 to try to get away. 

That’s just the beginning. To enter the world of Mortal Engines, you also have to wrap your mind around the idea that an evil leader could create a massive weapon occupying much of the city’s center while keeping it a secret from his fellow citizens and his higher-ups.

Suffice to say, there are more big leaps required at Mortal Engines than at the Summer Olympics.

But here’s the thing: Once I accepted its deeply implausible basic concepts — as laughable as they are — I enjoyed spending time in this steampunk-ish world.

At the center is Hester Shaw (Hera Hilmar), who makes her presence known early on by attempting to assassinate Thaddeus Valentine (HugoWeaving), one moustache-twirl-credit short of graduating from Obvious Villain University.

Shaw’s efforts are thwarted by good guy Tom Natsworthy (Robert Sheehan), a museum geek interested in ancient technology while aware of its dangers. There are more key characters as well but none likely to inspire action-figure collecting …

… except perhaps Shrike (Stephen Lang), the most unique creation in Mortal Engines. Resembling a zombified T-800, he’s a creature whose backstory weaves with Hester’s in interesting ways. The payoff here — like the action payoffs later in the film — don’t quite hit the mark but neither do they hit the wall.

Context may have tempered my reaction. After recently watching 30 or so films vying for Oscar consideration, it was refreshing to witness one with no such ambitions.

Even in the world of science-fiction and fantasy epics, it seems content to be “good enough.” Mortal Engines doesn’t have the“we’re walking … we’re walking … we’re fighting … we’re walking” heaviness of the Tolkien films (on which first-time director Christian Rivers worked as a storyboarder and visual-effects supervisor) and its characters don’t pop the way the Star Wars crew did in its first cinematic outing. It doesn’t have the wild originality of Valerian and the City of a Thousand Planets, but it also doesn’t have that film’s sexist core and annoying lead male. The pretensions and cinematic plagiarism of Avatar are nowhere to be seen and it isn’t nearly the misfire that John Carter proved to be.

It’s easy to dismiss as Waterworld with wheels — for those who forget Waterworld was actually kind of fun — but it also doesn’t seem to aim to be more. Mortal Engines doesn’t take itself too seriously and, on the flipside, doesn’t get cute by winking at the audience. It doesn’t break the action for whimsy and it’s got female characters ready and willing to unapologetically kick ass.

For those of us who yearn for non-franchised science-fiction entertainment — and for those willing to take those big leaps — Mortal Engines is a good-enough oddity.