Most of us think that Obsessive Compulsive Disorder (OCD) is just over fussy tidying. But it's actually much more serious. Sophie has to check that she hasn't killed people, looking for dead bodies wherever she goes, Richard is terrified of touching the bin, and Nanda is about to have pioneering brain surgery to stop her worrying about components on her body - that her eyebrow might not be aligned or that she has bad breath. Professor Uta Frith meets the people living with OCD, looks at the therapy available and asks what neuroscience can offer by way of a cure.