“Pride and Prejudice and Zombies” is as silly as it sounds, and not nearly as fun as it should be.

In this adaptation of Seth Grahame-Smith’s best-selling genre mashup of Jane Austen’s classic and, well, zombies, the Bennet sisters don’t just have marriage and love and class obstacles to fret about — there’s also the imminent threat of the undead overtaking the land. Here, the Bennet sisters aren’t merely unmarried gals looking for a suitable match, either. They’re trained warriors who can and do protect their homestead. The most passionate, of course, is Elizabeth (“Cinderella’s” Lily James).

Early on the girls (Bella Heathcote, Ellie Bamer, Millie Brady and Suki Waterhouse) get to show their blade-wielding might against the fast-moving, brain-craving predators.

It’s actually pretty enjoyable, if a little manic.

But director Burr Steers’ attempts at melding these genres into one coherent film are clumsy at best. The film adheres sincerely to the beats of Austen’s story — the balls, the scheming, the misunderstandings between Lizzie and Mr. Darcy (Sam Riley), the iconic scenes — while peppering most with a zombie scare or two.

There is some wit in the simpler moments — a stoic shot of the Bennet sisters in the living room cleaning guns in their day dresses, for example, or the few famous verbal showdowns that are choreographed as all-out fights. But that’s the best that Steers can do to integrate the two very disparate tones sincerely.

Otherwise it feels as though we’re watching a number of movies patched together. Matt Smith and Lena Headey, in particular, seem to be acting in their own Terry Gilliam film that was kept secret from the rest of the cast.

James is the anchor of the film — as she should be — but she is really the only one with any verve or conviction at all. It makes up for a lot of the film and the story’s deficiencies, but ultimately not enough to save it. Riley’s Darcy is a growling bore for most of the film and the others barely register at all.

This story might have been better suited to a television adaptation. The characters would have been allowed to breathe for a beat in that case. Here, the action and violence take up the space that would have generally been used for character development.

That this film is rated PG-13 is a questionable decision, too, with all the skull smashing, head chopping and gut thrashing. With its literary origins and promise of some butt-kicking female protagonists, the story seems perfect for a younger audience. But Steers and company went dark and violent — still not enough for the horror crowds. And, save for Elizabeth, the warrior ladies really only get that one scene before letting the male soldiers take up the zombie fight.

The choice of Steers as director is perhaps the most peculiar of all. Directors can and should reach outside their comfort zone, but to go from “Igby Goes Down,” “17 Again” and “Charlie St. Cloud” to this might have been a side step too far. The Austen scenes are fine, but the action and horror don’t land. Steers reverts to jump scares and the odd technique of blurring the shot to show a character’s panic when a zombie attacks to dizzying effect. A simple cut would have sufficed.

The film is all over the board stylistically and tonally, and the elements of both horror and comedy fall flat. By the climax you’ ve almost forgotten what you’re watching and who you’re supposed to care about.

For now, it seems only Edgar Wright has really conquered the modern genre mashup. But that’s an unfair standard for any mortal, or undead, to live up to.