"The Descent" does just about everything right that "The Cave" did wrong, and hallelujah for that. There are plot similarities between the two—both detail a cave expedition that goes horribly awry when the spelunkers get lost and are subsequently stalked by ghoulish underground dwellers—but it is in the all-important area of filmmaking craftsmanship that makes them as different as night and day. "The Cave" was one of 2005's worst, the type of incoherent, tension-free dud that takes the wind out of the sails of horror lovers and makes the viewer wonder if newborn apes rather than human beings were handed a camera to make it. "The Descent" is a claustrophobic nightmare sprung to life, driven by a stark realism made increasingly unsettling when even its otherworldly elements turn out to be freakishly plausible.

It has been one year since Sarah (Shauna Macdonald) lost her husband and daughter in a tragic auto accident. In an attempt to try and move on, she agrees to a weekend getaway deep in the Appalachian Mountains with five friends and acquaintances. What starts off as a fun, physical day trip to explore a well-documented cave takes a turn for the worst when one of their passageways collapses and they become trapped. Worse still, daredevil caving know-it-all Juno (Natalie Mendoza) confesses that they aren't even in their intended tourist-attraction cavern, but one that, to her knowledge, has never been stepped foot in before. Unsure if there is even another way out, Sarah, Juno, the faithful Beth (Alex Reid), stepsisters Rebecca (Saskia Mulder) and Sam (MyAnna Buring), and wild child videographer Holly (Nora-Jane Noone) have no other choice but to press forward. As fear and paranoia take over for the girlfriends, Sarah catches a glimpse of someone or something in the distance. Juno insists it's her mind playing tricks on her, but Sarah knows what she saw. Soon, their survival will hinge on a lot more than reaching the surface.

Written and directed by Neil Marshall (2002's cult fave "Dog Soldiers"), "The Descent" becomes so enthralling and intense that perspective viewers shouldn't be surprised if they forget to breathe for minutes at a time. A perfect world would have had this UK export being advertised in U.S. television ads and trailers without even a hint that bloodthirsty creatures fall into the equation. They don't make their first appearance until the halfway point, which would have been one of the most chilling plot surprises in recent years. Alas, they are all over the marketing campaign and anyone coming to see "The Descent" will know basically what to expect. What these same audiences can't expect is that the creatures—actually billed as Crawlers and suggested to be humans that have evolved into blind underground cannibals who hunt through their sense of sound—aren't even the scariest part.

No, what is most frightening is the feeling of hopeless isolation Marshall evokes from the quandary of being lost in a dark, foreign place, and the effect this has on human behavior and relationships. The first act inside the cave is the film's strongest section, as the girls climb and crawl deeper and deeper. Before anything has even really happened, writer-director Neil Marshall, aided invaluably by Sam McCurdy's moodily suffocating cinematography and Simon Bowles' eerie and believable production design, suggests through camerawork, unhurried editing and the power of silences the possibilities of grave danger these six friends are bringing upon themselves. The same is true after their fates take a downward spiral and they must hang on to the belief that the cave has more than one exit.

Bringing the added threat of murderous living beings into the fold certainly ratchets up the stakes again, provocatively affecting each of the characters in highly diverse ways. As their fight-or-flight response takes over and friendships are tested under unthinkable circumstances, the already-fragile Sarah's psyche begins to crack, Juno must carry a terrible secret with her, and Rebecca and Sam will do whatever is necessary to stay alive. In Sarah's case, who senses death is imminent, she begins hearing the presence of her deceased daughter over her shoulder. Whether there is really anything there or it is simply another part of her fractured mindset is left to interpretation. For what is essentially a down-and-dirty genre pic, Marshall thoughtfully places just as much emphasis on the internal drama of the characters as the external, invigorating the proceedings with a layer of weight it wouldn't have had if the makers of "The Cave" had been in charge. It also helps to have a cast of six able and willing female actors, all of them more or less unknowns, to bring their characters' individual turmoil to life. They look like real people rather than models, and their earthy qualities make them largely accessible and sympathetic.

On the basis of the story's supernatural currents, the film's most indelibly bloodcurdling moment has no gore or violence at all. Instead, Marshall relies on the ultimate powers of suggestion, subtlety and simplicity when Sarah spots for the first time one of the Crawlers, hunched over and gnawing on something at the end of one of the cave's tunnels. It is one of this year's most haunting cinematic images—the stuff bad dreams are made of—but a little bit of its created apprehension softens once the Crawlers take a bigger role and are seen more often. The basic stalk-and-slash (or in this case, bite) sequences grow repetitive after a while, and the villains might have been better to stay off-camera for longer periods so that they remained mysterious. No matter, jittery suspense is consistently prevalent and certain shots and ideas owe a debt of gratitude to 1979's "Alien," which Marshall pays fond homage to.

If the distinctly accurate portrayals of human nature—its bleak side as well as its resilient and empathetic—is the highlight over the conventional monster movie-inspired horrors, then that is but another testament to the tightness of Neil Marshall's straightforward script. Serious and smart about its high-voltage scares and oppressive atmosphere, "The Descent" is a harrowing experience and a genre enthusiast's best bet in a summer of wimpy PG-13 fluff. This one knows how to get the job done, and it isn't afraid to tear up bodies, shove spikes in people's necks and crack some bones to do it.