Yorkshire police officer Ronald Craven is returning home with his daughter Emma having picked her up from a meeting of an environmental organization at her university campus. On the doorstep of their home Emma is shot dead. The police concentrate their effort on the theory that her murder was a botched attempt on Craven's life by a criminal he had been responsible for convicting. However, as Craven goes through Emma's belongings, he discovers a Geiger counter and a gun. He also learns that Emma's body and her possessions are radioactive. Travelling to London to assist with the inquiry, he is contacted by Pendleton, a polished official "attached to the Prime Minister's office", who informs him that Emma was known to them as a terrorist and that it was she, not Craven, who was the gunman's target.