At the seaside dealing with his late aunt Jane's estate, Scotland Yard Commander Adam Dalgliesh learns that a serial killer, known locally as the Whistler, is on the prowl. The local policeman in charge of the case, Tony Rickards, seeks his advice. He also meets a number of the locals including someone who works at the local nuclear power plant who alludes to safety issues and an anti-nuclear activist who seems bent on raising a ruckus.
When another dead woman is found, many assume it is the work of the Whistler. Discovered by Miles Lessingham while on his way to Dr. Alex Mair's home for a dinner party, the woman had been strangled and was lying just off the road. The victim was Christine Baldwin, an employee at the nuclear facility. Still worried about the computer virus and the impact it could have on the safety of the nuclear reactors, Toby Gledhill decides to join the anti-nuclear movement. Hilary Robarts is trying to evict the Blaney family from her cottage. Alice Mair is still haunted by the abuse she suffered as a child.
Walking home late one night, Commander Dalgliesh discovers the body of Hilary Robarts. The killing has all the hallmarks of the Whistler's work but this is now the second woman from the nuclear plant to be killed. Ryan Blaney was out walking at the time and doesn't have much of an alibi. Likewise, Caroline Amphlett, another plant employee, pressures a colleague to provide her with an alibi. As Chief Inspector Rickards questions the dead woman's colleagues and acquaintances, Dalgliesh learns that Toby Gledhill has disappeared.
With Toby Gledhill's suicide, there is one less suspect in the mix. No one is quite sure why he killed himself, let alone in such a public manner, but most are putting it down to a breakdown of some sort. Chief Inspector Rickards continues to interview various suspects and possible witnesses and is starting to find holes in many of their alibis. Dalgliesh gets some interesting information about Caroline Amphlett including the fact that she has purchased a large boat and is stocking it for seems to be a long voyage. Her boyfriend, Jonathan Reeves, questions the wisdom of having provided her with an alibi. Ryan Blaney's daughter Theresa has an appendicitis attack and fearing that she might die, tells her father that she has something important that she must share with their parish priest.
While strolling on the beach, Adam Dalgliesh comes across a tramp who is wearing relatively new trainers that may match some of the footprints found at one of the murder sites. The computer virus in the nuclear facility's computer system is getting out of control and they are forced to take the reactors off-line. Miles Lessingham sees a reason for Alex Mair to want Hilary Robarts out of the way. Jonathan Reeves travels to London to see what he can learn about Caroline Amphlett. While he learns little, it turns out she has quite a bit to hide. The Whistler commits suicide in a local seaside hotel and is identified as local handyman Neville Potter. He leaves a note for Dalgliesh claiming he is not responsible for Hilary Robarts' murder.
Caroline Amphlett's true purpose in working at the nuclear plant is revealed and Dalgliesh confers with the Security Service on the next steps. It is not clear however who it is that rammed her boat. Chief Inspector Rickards is ready to close the Robarts murder case as unsolved but Dalgliesh urges him to continue and provides his own profile of the killer. Meg Dennison's alibi is weak and she clearly wasn't at home when she claimed to be. Theresa Blaney is at home recuperating and reveals to Alice Mair the identity of the person she saw at the beach the night Hilary Robarts was murdered.
