Marnie has a form of OCD called Pure O, which manifests as constant invasive thoughts about sex. But this comedy-drama never resorts to cheap laughs. It is brave, bold and barely short of a miracle Marnie, the 24-year-old heroine – and I use the word advisedly – of new drama (or comedy-drama, possibly, but one that really wrenches its laughs out of darkness) Pure, suffers from a very specific form of OCD. Called Pure O, it manifests not as external physical acts such as compulsive handwashing or repeatedly checking things, but as powerfully intrusive thoughts, often about subjects considered taboo; such as violent, even murderous, acts or – as happens in Marnie’s mind, brutally colonised by the condition 10 years ago – sex. We meet Marnie (played by newcomer Charly Clive) shivering by a roadside after fleeing her parents’ wedding anniversary party. During her supposedly celebratory speech, which begins as an ordinarily exquisite agony for us all to watch, her treacherous thoughts str...