Claire finally loses herself in the hum as the outside world closes in on the group. One last group session ends in tragedy.

Unable to experience the hum the way the others can, and increasingly guilty about her relationship with Kyle, Claire has a crisis.

Claire and Kyle discover a group of other people who not only can hear the hum but want to embrace it. However, Kyle's mother finds out about their meetings.

On an ordinary day, Claire Kutty, a secondary school English teacher in her early forties, hears a low, rumbling sound while driving her daughter Ashley to their school. This innocuous noise starts to cause Claire migraines, nosebleeds, insomnia and even visions. No obvious source or medical cause can be found – and no-one else can hear it.

After weeks of feeling increasingly isolated and on edge, Claire is approached by one of her students and Ashley's classmate, Kyle Francis, who tells Claire he can also hear the sound.