After the success of the first “Paranormal Activity,” the $15,000 independent supernatural thriller that Paramount picked up for distribution in 2008 and marketed into a major genre hit, it was inevitable that a sequel would follow. Oren Peli, who wrote, directed and edited the first picture, is only a producer on this one, but “Paranormal Activity 2” piggy-backs on its predecessor—in terms of both style and narrative—in a positively slavish fashion, which is both its virtue and its curse. It gives fans what they want—more of the same—but inevitably the law of diminishing returns comes into play.

As written by a trio of scripters, the movie manages to be not only prequel and sequel, but a “contemporary” as well. The original was about Katie and Micah (Katie Featherston and Micah Sloat), a twentysomething San Diego couple whose house is invaded by a demon whose activities while they sleep at night the man records on a video camera. The experiment does not turn out well.

Here, the focus is on Katie’s sister Kristi (Sprague Grayden), who moves into another San Diego house with her new husband Daniel (Brian Boland), their infant son Hunter (William and Jackson Prieto), and Dan’s teen daughter Ali (Molly Ephraim)—as well as the family dog, a German shepherd called Abby, and nanny Martine (Vivis). They’re occasionally visited by Katie and Micah, and one of the many chronological titles that punctuate the action informs us that one visit comes sixty days before Micah’s death, with which the first picture ended.

Before long, the Reys begin to experience poltergeist-like phenomena. The house is ransacked one night, though nothing is stolen but a necklace Katie had give Kristi. Dan installs security cameras as a precaution, and the rest of the picture is supposedly shown through their footage. Loud thumps occur in the night, and the mechanical pool cleaner mysteriously leaves the water every night. Doors and drawers open and close on their own, and pots and pans fall from their kitchen hooks with a clatter. Martine swears evil forces are at work, but the rationalistic Dan dismisses her for her superstitious ways, while Ali speculates that the spirit at work might be benign—her dead mother, perhaps—but soon changes her tune when her boyfriend brings over Ouija board one night and the force locks her out of the house.

The phenomena get increasingly violent, of course, and there are casualties. But by and large the picture, like the first, avoids the sort of graphic, gory stuff so common in other horror series in favor of shocks—or “gotcha!” moments if you prefer—that leave a good deal to the imagination. The script provides an explanation of sorts for what’s happening in a brief allusion to Katie and Kristi’s childhood, but it’s a pretty dumb one. It does, however, offer an amusing final twist in the way in which Dan and Kristi rid their home of the unwelcome presence, and the unforeseen consequences (which in turn take us back to, and go beyond, the ending of the first movie).

When “Paranormal Activity 2” works, it’s because it follows the template of its predecessor. But the tricks are necessarily familiar, and while loud noises and slamming doors can still make you jump, they carry less resonance the second time around. Director Tod Williams tries to give things urgency—and occasionally succeeds—but he can’t do much with the drab dialogue, one-dimensional characters, or thoroughly pedestrian (supposedly “naturalistic”) acting. (Abby frankly has more personality than any of the humans, save maybe little Hunter. Neither says a word, of course.) And paradoxically the fact that this is a slicker movie, with a bigger budget, makes it less effective. Even the extra-shaky camerawork at the start seems like an exaggerated homage to the bare-bones style of the original than a stylistic necessity.

The only real cleverness in “Paranormal Activity 2” lies in the way it folds its story into the first picture and becomes one with it. Otherwise it’s the sort of retread that may momentarily please fans of the original, but by the end it’s come to seem an unnecessary addendum that wears out its welcome long before it reaches the close of its relatively short running-time.