A couple, Josh and Renai Lambert (Patrick Wilson and Rose Byrn) and their two sons are being haunted in their new house. When this continues they move but the spirits are still following them. Their oldest son goes into a coma and months go by. They find out, with the help of a medium, Elise (Lin Shaye), that the boy is haunted. He has out-of-body experiences at night, when he sleeping, and had just thought them dreams. But he went to far and now his mind is lost in the other realm, "the further". Now, the spirits are drawn to his comatose form, wanting to take over the boy's body. The most malevolent creature is this spirit that looks like Darth Maul from the STAR WARS movies. It's up to the parents to somehow get their son back, which is a bit like a sequence in A NIGHTMARE ON ELM STREET. And, of course, there's this whole nod to the ghost investigators in POLTERGEIST.
This is one of the creepiest horror flicks of the decade, with some truly frightening scenes. This is taken down a notch by some inane dialogue and stupid things the characters do but doesn't detract too much from enjoying the movie. INSIDIOUS also, features a brief role by Ruben Pla as a doctor (interviewed a while back on buried.com), as well as screenwriter Leigh Whannel as one of the ghost investigators.