In the film, Katie and her boyfriend Micah (pronounced MEE-kah, not MY-kah) have moved into a house in San Diego, and have apparently been followed by something from Katie's past. Katie always saw it as a shadow at the edge of her bed, saying her name, but now it's begun to take a more direct approach to gain their attention. To aid in identifying whether or not it's really there, Micah sets up a video camera to record the house while the couple is awake, asleep, and even not home. In the beginning, the things that happen are fairly standard for a haunting; a door moves, a light kicks on while footsteps come up the stairs, then off again as the footsteps reach their mark.
A psychic comes to the house at Katie's behest to see if there is anything he can do, asks the couple a number of questions, identifies that the spirit plaguing them is not a ghost (the lingering spirit of a human life) and is, in his terms, a demon (a malevolent non-human spirit) that probably wants Katie herself. Micah suggests that they should get a Ouija board and attempt to find out what the thing wants, but the psychic firmly warns against the idea, as making an attempt to contact it, and play its game will only be taken as an invitation. Micah initially expresses an intent to ignore this advice, but Katie finally demands a promise from him, and he promises not to purchase a Ouija board.
As the nights progress, Micah, who consistently swears that he's helping, and has "got a handle on this, and I'm going to fix it..." mostly just follows Katie around the house with a camera, sets the camera on the tripod in their bedroom at night, and says a lot of things to egg the demon on. "Come on out there, we haven't seen anything interesting tonight. We think you're gone, but why don't you show us if you're still here!" (The night that the lights started working, and the footprints became clearer, more distinct.) Frankly, he's an idiot, and winds up doing a lot more damage than he realizes. For the rest, go see the movie, but I recommend picking up a set of Depends on your way to the theatre, or at the very least, visit the bathroom before you take your seat. Absolutely one of the scariest things I've ever seen, and very, very well-timed, well-paced, with an ending that ought to creep you out enough to be afraid to go downstairs by yourself. I know I sure am...
A moment to rant at the character: Perhaps it's because I've been a witch for almost ten years (surprise, to those who didn't know that one) and perhaps it's just because I'm an extreme nervous case who has seen dozens of horror films and occasionally watches those haunting shows on television, but the very first thing that I would not do is tell the thing I wanted proof it was in my house. Helping? That's not helping. That's doing precisely what you were told not to do, which was play games with it and invite it in. "...show us if you're still here..." is an invitation, is it not? If you want to help, read something other than a cheap Dover re-printing of a publication from the 20's. Pick up The Complete Idiot's Guide to Ghosts and Hauntings or something written with a slightly more modern-day perspective. Take a page from the Native Americans, and burn some sage (raising the vibrations in the area, warding off unpleasant energies and spirits). Do...not...FUCKING...talk...to...it! /end rant