It's kind of an ugly mirror, and that's reason enough to not drag it home, but tightly wound Kaylie (Karen Gillan) does, and invites her brother Tim (Brenton Thwaites), just out of a mental institution, over to look at it. See, 11 years ago, this mirror was in their dad's office, and, as we see in an extended flashback narrative, it might have caused some horrific abuse and killings. Or maybe Kaylie and Tim share some kind of false-memory syndrome, perhaps in response to long-ago family troubles. (Oculus is reminiscent of old EC Comics stories, which often used mundane objects and family tensions as a springboard for horror.)
For a while, Mike Flanigan's film flirts with this tension between reality and perception before committing to a side. Along the way, there's a bit of grossness (biting into a light bulb, always a bad idea!), but this horror film is fairly restrained, and doesn't rely on cheap gimmicks like jump-outs and frenzied behavior. The ending is a bit of a letdown, and expect to see Oculus 2.