Before it careens off the rails halfway through its slender 90-minute runtime, The Strangers treats moviegoers to what may be the creepiest opening act of any American-made horror film in recent memory. The set-up is beautiful in its simplicity: While spending the night in an isolated country house, a young couple (Scott Speedman and Liv Tyler) is menaced by a trio of mask-wearing psychopaths. Sure, that same premise has been employed by any number of forgettable slasher flicks, but what sets The Strangers apart, at least for the first half-hour, is its stillness. Writer-director Bryan Bertino eschews the smash-cutting and shaky Steadicam shots that typify the genre's current house style for a slower, quieter pace designed to unsettle the audience rather than satiate their bloodlust.

In fact, some of the scariest moments in the first act of The Strangers involve things we don’t see—a booming knock on the door, an unfamiliar creak in the hallway, a stranger on the porch whose face is cloaked in darkness. All of this builds up to the film's money shot, which is featured prominently in all of its trailers as well as the theatrical poster: As Tyler stands in the middle of the living room, a man in a mask shuffles silently out of the shadows behind her and pauses there, not moving, not talking, just watching her, as if he has all the time in the world.

That lone image taps into a primal fear that many horror films never even come close to reaching. After all, few experiences are more terrifying than being awake in the dead of night and feeling like someone (or something) is in your home with you. Most of the time, these fears turn out to be groundless, but that doesn't make those seemingly endless moments before you work up the courage to turn on a light or look over your shoulder any less paralyzing. Only a handful of movies, most memorably Roman Polanski's still-potent Repulsion, have been able to sustain this kind of tension from start to finish, and for a little while anyway, it looks like The Strangers might join that rarified company. Even after the three boogeymen go from being bumps in the night to corporeal beings, Bertino continues to use them sparingly at first, instead keeping his camera locked on the two victims, giving viewers little respite from their panicked faces. Too many contemporary horror films are happy to treat the characters as meat waiting to be slaughtered and while those kinds of gore-fests have their place, there's something to be said for a movie that doesn't invite you to automatically root for the axe-wielding maniac.

Unfortunately, at a certain point, The Strangers devolves into the kind of generic chase picture that slasher flicks frequently become. Once Tyler and Speedman leave the house and start alternately looking for and running away from the killers, the ominous mood of the first act is shattered and we're left to mark time until the gruesome climax. The heavy-handed score—credited to the duo tomandandy, who previously penned music for The Mothman Prophecies and The Hills Have Eyes remake—also hurts the proceedings, telegraphing scares and underlining every "boo!" moment with a distracting sting when simple silence would be far more effective. The shift in style is so abrupt, one can't help but wonder whether the film was taken out of Bertino's hands and reworked into what the studio thought would be a more audience-friendly form. (The final scene in particular seems like the kind of stock "surprise" ending that executives believe moviegoers automatically adore. Here's a hint: We don't—especially when it doesn't make a lick of sense.)

Of course, it's equally possible that the first-time feature filmmaker never really decided where he wanted the story to go after the first 30 pages and wound up settling for the path of least invention. Whatever the reason, it's a shame to watch a film that begins with so much promise collapse on itself. For now, the search for the next great American horror movie continues.