Twenty-four year old Marnie 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, Marnie finds a gang of new friends, all with their own foibles. She moves in with her deceptively cheery old school friend Shereen. She befriends Charlie, 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 Marnie’s new gang is journalist and ladies-woman, Amber who has been gaining a problematic rep. for her promiscuity. Then there’s Amber’s housemate, the irresistible and unassuming Joe whom Marnie shares a Will they-Won’t they romance.
Marnie jumps on a bus to London on a mission to change her life and figure out what is wrong with her. Alone in the big city, she tumbles into the lives of Shereen, Amber and Joe.
Marnie hits another dead end when she goes to a sex addicts meeting, but she finds an unexpected kindred spirit in recovering porn addict Charlie.
Marnie is determined to make the most of being a single Londoner now she knows what is wrong with her. She jumps into bed with Benji an earnest, clingy barista, but it has consequences at her work.
Marnie and Charlie try to pick themselves back up after hitting rock-bottom. Marnie gets help from an unexpectedly understanding Shereen while Charlie tries to prove he's up to his old job.
Encouraged by her new therapy, Marnie tries out trusting her old friend Helen with her secrets and brings her two worlds together at a big dinner party. What could possibly go wrong?
Marnie is shaken when she realises she's pushed Shereen too far, and starts to become paranoid that everyone has turned against her now they know about her condition