A 24-year-old woman, Marnie, struggles with intrusive and disturbing thoughts due to her obsessive compulsive disorder, "pure O". She escapes her daily life by traveling to London, where she finds a group of misfit friends, each with their own personal struggles. Her new friends include an old school friend, Shereen, a recovering addict, Charlie, and a promiscuous journalist, Amber, and her housemate, Joe, with whom Marnie develops a romantic connection.
Marnie has been plagued by disturbing sexual thoughts for as long as she can ...