Claire Kutty, a secondary school English teacher, hears a low, rumbling sound while driving her daughter Ashley to their school; after some weeks, Kyle Francis, tells Claire he can also hear the sound.

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.

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

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

Final episode. Siobhan turns up at Jo and Omar's house, demanding they send Kyle out. When the group refuse to cooperate, she calls the police. As the outside world closes in on the group, one last session ends in tragedy...