This unsettling black comedy about private passion and public shame is based on Zoe Heller's acclaimed novel, adapted for the screen by celebrated dramatist Patrick Marber (Closer).When art teacher Sheba Hart (Cate Blanchett) arrives at a London comprehensive she catches the keen eye of her older colleague Barbara Covett (Judi Dench). Barbara is not the only one drawn to Sheba, who then begins an illicit affair. Barbara is the keeper of Sheba's secret, but can she be trusted?