In his latest novel, Billingham echoes the life of Myra Hindley, the English serial killer who--in partnership with Ian Brady--hatched plans of rape and murder. Billingham's hero, Detective Tom Thorne, faces his own Myra Hindley when his Homicide Assessment Team is dispatched to the location of an apparent suicide at Highgate underground station. Tom watches in horror as those still working on the tracks gather up what was is left. There was nobody close to the woman, and the CCTV evidence is pretty clear-cut.

Mary Fulton is puzzled by her sister's suicide. Ella, Phillipa's niece, has no idea what might have made her aunt want to take her own life, despite her having just been dumped and being extremely unhappy. Tom's instinct tells him that Phillipa Goodwin was the victim of a murder and that Patrick Jennings, the man both Mary and Ella had mentioned in the car, is responsible. He was charming--"a bit of a silver fox"--but simply disappeared one day and cut Phillipa off. Tom's trusty colleague Nicola Tanner (who has a great side story of her own) is quick to take a look Philippa Goodwin's finances while Tom tries to convince the formidable DCI Russell Brigstocke that Patrick Jennings is to blame, that he "murdered Phillipa in a different way."

At the beginning of the investigation, Tom's team need to prove pre-meditation: not just that Jennings was a fraud and a confidence trickster but that he embarked on a systematic campaign of carefully planned psychological abuse--and that this abuse played a significant role in Pip's decision to kill herself. In the seaside town of Margate, Tom tells Phil Hendricks about Phillipa's strange suicide, about the man who destroyed her innocent life. There's a small window of opportunity granted to them by Brigstocke, but Jennings has covered his tracks and "probably done it plenty of times before." Tom dreams of killers and rapists, about men who hate and hurt, about "monsters." He asks himself how a "run of the mill con-artist" could possibly be the same man who used a rock to bludgeon 17-year-old Kevin Deane to death yet still take great care to stay elusive and keep his real identity hidden.

As Tom and Nicola race to unlock the case, the narrative switches to Sarah, who likes to sit with other mothers while having coffee and cake outside St. Mary's School, where the main aim is to get "her boy Jamie's name down nice and early." Here she meets a man with a silvery goatee beard who smiles automatically at her. She meets "Conrad" at a time when she's reckless to abandon herself to the power he so obviously has to transform her and create a different kind of quickening desire: "it's ridiculous and feels so much more overpowering."

Sarah's twisted psyche is matched only by Conrad, who spends frantic months trying to impress her. Like Hindley and Brady, Sarah and Conrad seem to be the perfect model of "folie a deux," the madness of two--a "weird chemistry" that creates delusions or even exaggerates the delusions that are already there. Lying next to Conrad, Sarah freezes when he says

[a] version of something she lives in terror of hearing, daily; the knowing remark, the veiled suggestion from this busybody or that concerned parent.

There's little about this case that isn't weird, off-kilter and even unnatural, "as though something misshapen had woken and had begun crawling towards him into the light." Tom has had this feeling ever since that morning at Highgate tube station when he watched Phillipa's body-bag being lifted from the tracks. Though Billingham's skill at conveying two crazed serial killers makes this novel soar, Their Little Secret (A Tom Thorne Novel) works best when it delves into the enduring connection between Tom Thorne and Nicola Tanner. Nicola, still suffering from the death of beloved Susan, is a powerful voice, a singular woman drawn to Tom--obviously not in the romantic sense, but as a professional equal. She knows Tom's tenacity in cracking a murderer's puzzle. She wants to use him to really push forward and break out of Susan's shadow.

And what of Ella's surprising, twisted narrative? She shames Thorne over the "ridiculous romantic things" he thought about her that day they drank tea in her flat and talked about art and murder. Did Ella know what she was doing? Was she aware of the impression she had on Tom? Plummeting us into the gritty life of London and Margate, Tom's investigation becomes even more macabre when the forces of two crazy serial killers threaten to embark on what could be one giant killing spree.