Set in Victorian England during a freezing winter, Inspector William Monk is back working for The Thames River Police after some previous mishaps with his former employers, The Metropolitan Police. It is his misfortune to watch the suicide of two people as they plunge into the icy water from a bridge over the river Thames. But was it suicide, was it an accident or was it murder? Identifying the girl's body, it soon becomes clear that Mary's father, too, had committed suicide only a short while ago. Inspector Monk is troubled that two members of the same family should die in this way and when it further comes to light that the father worked for the company whose main directors are also related to both Mary and her sister, the plot, as they say, thickens. The body of the other victim in the Thames is one of these directors and Mary's fiance.
The company they worked for is currently building a new sewer system in the old and dangerous London underground, where hundreds of half-starved neer-do-wells eke out a precarious living. The pressure on the company to complete the excavation of tunnels is massive and soon Monk realises that the charming facade at company level is beginning to reveal a dark and ugly underbelly. The huge machines employed to dig out the tunnels may be dangerous and likely to bring down the collapse of the London waterway system.
Could this be a reason for keeping dissenters quiet since Monk begins to discover that Mary's father was murdered whilst voicing his concerns over this safety aspect and Mary had taken up the battle to continue searching. Was she, too, murdered in another cover-up attempt?
Monk brings in his enthusiastic and energetic wife to assist and with the help of one or two characters from the dark underground tunnels, they find themselves in deep danger as the killer intends that his secret will remain just that.
Monk has an investigative way that brings about the conclusion but the mystery is not revealed until almost the last pages and he certainly needed all the help he could muster as they close in on the real murderer.
This report prepared by michael watson