Lily Lidbury is a charismatic headmistress idolised by both parents and children of Belgrave Hall, an exclusive girls' day school in London. After more than a decade of celibacy, the upright Lily embarks on a perilous affair with Benton Anderson, an investment banker and father of one of her pupils. She risks blowing the lid off her sparkling career and the well kept secret of her own past which threatens to overwhelm her. The pupil is an American child with red hair, sea-green eyes and matching velvet coat that reminds her of her own dead daughter. In a state of erotic euphoria and shame, Lily begins to lose control. Her mind focuses more on her lover than her work, and her ruinous errors of judgement portend letting everyone down.