Twenty-four-year-old Marnie is witty, smart and ‘normal.’ Well, ‘normal' apart from the relentless noise inside her head, forming an incessant barrage of graphic x-rated thoughts. Unbeknown to Marnie, she’s caught in the grip of a remarkable form of obsessive compulsive disorder – nicknamed ‘Pure O’. After vividly imagining her parents engrossed in an orgy, Marnie packs a bag and jumps on the first coach out of Scotland to London. A story of self-discovery, finding friends and learning how to love, Kirstie Swain’s funny, emotive series is based on Rose Cartwright’s acclaimed biography.