It may well be marketed as a straight horror film, but this is much more than that. It pretty much ticks every plot point you would expect from a film about possession, yet this still stands out from the pack. Part of this is down to the structure of the film, with a self contained story that doesn't pander to the possibility of sequels or final twists and presents both supernatural and medical reasons for the titular character's condition. This conceit is very effective with the flashback sequences suitably creepy and then turned on their head moments later. It is to the film's strength that the audience is largely left to make up their own mind regarding Emily's condition (this being ostensibly a horror film, it can't quite commit to not favouring the supernatural). The central two leads of Laura Linney and Tom Wilkinson lend some gravitas and credibility to the film, building on the themes of faith and belief within that are perhaps best summed up by a final courtroom speech from Linney. Jennifer Carpenter is also fantastic in a dual role which requires her to earn the audience's sympathy and fear. Well worth the time to seek this one out!