South London detective Sarah Mason is a single mother. She and her ex-husband, fellow detective Graham Boyd, adore their 15-month-old daughter Molly. But Sarah's world falls apart when she receives a devastating threat - her daughter has been taken and the abductor plans to raise Molly as their own. To save her daughter, Sarah must take matters into her own hands, in a desperate hunt that will take her to the very depths of London's underworld.