For a policeman, there are some questions that have to be asked even if you don't want to know the answers . . .

A middle-aged man jumps under a tube train at Shepherd's Bush station, and a teenage girl is killed in a hit-and-run, in a country lane puzzlingly far from her home on the White City Estate: two unrelated incidents which occupy DCI Bill Slider and his team during a slack period. At least it's a change of speed after the grind of domestics, burglaries and Community Liaison.

But links to a cold case - another dead teenager, pulled out of the River Thames - create doubts as to whether they are indeed unrelated. And slowly a trail of corruption and betrayal is uncovered, leading Slider and his firm ever deeper into a morass of horror.