Some sins won't wash away ...

A summer of endless rain in the Peak District leaves the officers of Derbyshire's criminal investigation department with a problem. They have discovered a man's body lying in shallow water, but torrential downpours have swollen the rivers and flooded the roads, making travel difficult and forensic examination impossible.

And that's not all. The absence of Detective Cooper, on extended leave after an arson attack, has left a serious gap. Detective Fry is a reluctant temporary replacement, but now their makeshift team is about to be tested to the limit. The fatal events of one damp August night are likely to remain shrouded in mystery if they can't track down a car glimpsed only as a dark outline in the rain by a passerby.

When the drops turn into a deluge, loyalties among the officers will be put under intolerable strain as they try to solve their toughest case yet. And that's before it emerges that Detective Cooper is not at home recuperating, but has vanished into thin air ...