While lying in bed with her husband one night, Claire Devon hears a low hum that he cannot. Though no obvious source or cause can be determined, it begins causing her headaches, nosebleeds and insomnia, gradually upsetting the balance of her life. When she discovers that a student of hers can hear it as well, the two strike up an unlikely and intimate friendship. Feeling more and more isolated from friends, and family, they fall in with a disparate group of neighbours who can also hear the sound. What starts as a neighbourhood self-help group transforms into something extreme, with far-reaching and devastating consequences.