Twenty-four year old Marnie (Charly Clive) has bad thoughts all the time and she can't tell anyone. Her mind is XXX-rated and intrusive thoughts are piling up inside her head. She is caught in the grip of an excruciating form of obsessive compulsive disorder -nicknamed 'pure O' - where her obsessions take the form of intrusive sexual thoughts, and the compulsions are unseen mental rituals that deeply affect her daily life. Something. Has. Got. To. Give. At breaking point, she packs a bag and, with no plan, jumps on a coach to London. In the capital, Marnie soon discovers she's not the only one who's lost. On her search for herself, Mamie finds a gang of new friends, all with their own foibles. She moves in with her deceptively cheery old school friend Shereen (Kiran Sonia Sawar). She befriends Charlie (Joe Cole), who is in recovery, having torpedoed his love and work life, due to his porn addiction. He's now single, stuck with an old-school flip-phone and attends weekly Sex Addicts Anonymous meets. Queen among Mamie's new gang is journalist and ladies-woman, Amber (Niamh Algar) who has been gaining a problematic rep. for her promiscuity. Then there's Amber's housemate, the irresistible and unassuming Joe (Anthony Welsh) whom Marnie shares a will-they-won't-they romance.