Veteran paranormal researchers Dr. Margaret Matheson (Sigourney Weaver) and Tom Buckley (Cillian Murphy) debunk fraudulent claims of ghost whispering, faith healing and other psychic phenomena by detecting what Matheson calls "red lights," the subtle tricks behind every staged supernatural occurrence. But when the legendary blind psychic Simon Silver (Robert De Niro) comes out of retirement after 30 years, his once-fearless adversary Matheson warns Buckley to back off, fearing reprisal from the powerful Silver. Determined to discredit Silver, Buckley and his star student (Elizabeth Olsen) use every tool at their disposal to uncover the truth behind the charismatic, spoon-bending, mind reader. But Buckley is forced to reexamine his own core beliefs as his quest builds to a mind-blowing conclusion.