This feels almost like a throwback to the Amicus anthologies of the 70's, in which a haunted object brought terror and death to whoever owned it. Here, it's a mirror which is the item and question, and its victims include siblings Kaylie (Gillan) and Tim (Thwaites). Their first encounter with the mirror, 11 years ago, left them orphans and Tim committed to a psychiatric institute. Now, he has just been released, but won't be allowed to continue trying to repair his life, since Kaylie is intent on proving the supernatural and evil nature of the mirror, which has been taking place over centuries. She has returned to the house where tragedy struck, set up a scientific environment to prove her theory, and wants Tim to take part, so he can see he bears no fault for what happened previously. Conversely, he thinks she is using the occult as an excuse to avoid having to face the more banal truth. However, it becomes increasingly clear that she is right, and the mirror appears capably of creating fully convincing hallucinations, to make its victims do whatever it wants.
Seems this is an extended version based on a short film, and that makes a lot of sense, because it's a great concept, but one which doesn't have enough meat to fill an entire feature. It might have made more sense to go the Amicus route, and tell a number of stories based around the mirror: there is an element of that here, as we switch back and forth between Kaylie and Tim now, and 11 years ago, but it isn't enough to provide sufficient variety. Once it's established that anything may or may not be real, the viewer is left inclined to disbelieve everything, which severely limits the amount of resulting emotional commitment. The performances are fine: Gillan, previously best known as a Doctor Who companion, has no problems hiding her Scottish accent, and Thwaites does a good job of displaying mental fragility. I just get the feeling the short version, Oculus: Chapter 3 - The Man with the Plan, probably packed close to as much horrific impact into one-third of the running time.