The Thames is London's most important yet neglected artery. When a young woman is found chained to a post in the tide, no-one can understand how she came to be drowned there. That's only part of the problem; Bryant's deteriorating condition prevents him from handling the case. To make matters worse, May makes a fatal error of judgement that knocks him out of action. In an adventure that's as twisting as the river, will there be anything left of the Peculiar Crimes Unit when it's over?