'Oculus' (R)

Mirrors have been as much of a fixture in horror movies as knives and cats that suddenly jump from the shadows. But they’re best in cameos, as in the ending of Dressed to Kill or the room 237 scene in The Shining. Oculus revolves entirely around an ornate mirror that is, what, a gateway to hell? A summoning force for evil spirits? A really ugly piece of furniture from a medieval Pottery Barn?

One of the problems with director Mike Flanagan’s occasionally involving but ultimately dull thriller is that the whole movie hinges on a reflective piece of glass. As kids, Kaylie (Annalise Basso) and Tim (Garrett Ryan) watched their parents (Katee Sackhoff and Rory Cochrane) go crazy after a prolonged series of strange events that started when the family bought a mysterious antique mirror. Their mother died a gruesome death, and 10-year-old Tim had to shoot his father to protect his older sister, who was about to suffer a similar fate.

Thirteen years later, Tim (Brenton Thwaites) has been declared sane and released to the care of his sister (Karen Gillan), who is engaged and is leading a normal life except for her obsession with that damned mirror. She shows her brother all the research she’s conducted: The mirror is 14 centuries old and responsible for at least 45 deaths by supernatural forces. Most people at this point would stick it in a dumpster somewhere and be done with it. But Kaylie is intent on finding out what is possessing the antique, and she has set up a high-tech lab, complete with recording devices and heat sensors, to perform a sort of exorcism. She needs answers.

She probably also needs the same sort of psychiatric care her brother got. He relies on rational explanations for the strange goings-on and wants to move on. But Kaylie won’t be denied.

The first half of Oculus works surprisingly well. Gillan and Thwaites are immensely likable as the grown siblings, and when they argue and bicker, the dialogue doesn’t have that forced air of killing time typical in most horror movies. Flanagan also does something clever with the film’s structure, showing the young adults revisiting moments from their childhood by inserting them into the flashbacks (they’re literally watching themselves, which works better than constantly cutting back and forth between past and present). Before things start going crazy, Cochrane and Sackhoff make for a fine pair of parents (Sackhoff, so often cast as a tough chick after her killer run on Battlestar Galactica, is refreshing as a nice, cheerful mom).

The movie gradually reveals some troubling discrepancies in Kaylie and Tim’s recollections of the past: They don’t remember every event the same way. But once the main scenario has been established, Oculus becomes just another movie about good-looking young people trying to make sense of incomprehensible evil. (I mean, really, who does that?) Flanagan, who co-wrote the script with Jeff Howard, also overplays his hand. I can buy the mirror eating a dog, sure, and I liked how the movie reveals why no one can simply smash it. But I can’t get past the scene in which it pretends to be a 911 operator. Sometimes, you just have to draw a line.

As Oculus builds toward its gruesome (but not unexpected) finale, the characters get lost in a series of hallucinations and flashbacks that don’t amount to much other than eat up screen time. Worst of all, the film simply isn’t scary. Flanagan, who uses admirable restraint with blood and gore, is aiming for a psychological thriller more than he is trying to outdo The Conjuring. Even on that level, though, the thrills are about as scary as one of those out-of-nowhere cats.modest at best.

Cast: Karen Gillan, Brenton Thwaites, Katee Sackhoff, Rory Cochrane, Annalise Basso, Garrett Ryan.

Director: Mike Flanagan.

Screenwriters: Mike Flanagan, Jeff Howard.

Producers: Marc D. Evans, Trevor Macy.

A Relativity Media release. Running time: 105 minutes. Vulgar language, violence, gore, disturbing images. Playing at area theaters.