Whilst Detective Chief Inspector Nina Monroe sets out to investigate the murder of a prominent politician whose body was discovered on the banks of the River Thames, she is called upon to help a young woman who has been badly beaten. With the murder investigation deadlocked, her troubles are compounded when another high-profile politician is murdered. In an unexpected twist, as the investigation moves forward it becomes apparent to Nina that the girl's beating and the two dead MPs are linked and her only choice is to call upon the young woman to help solve the murders.