In Billingham’s terrific stand-alone novel, therapist Tony De Silva hosts his group of ex-addicts every Monday night. In attendance are anesthesiologist Robin, ex-junkie Heather, newly divorced but well-heeled Diana, who has drifted into alcoholism, and Chris, a gay man who battles with substance abuse while living in a series of hostels and shelters. Also in the group is Caroline, a food-addicted newcomer. The crucial commonality between these men and women is their lack of trust and their inability to cope with the world around them. A respected doctor, Tony also has a history of addiction to a variety of available medications.

Tony’s aim is to have the group work on a range of recovery skills and to address the shame that drove them towards substance abuse to begin with. But what begins as an exercise in talking about their current lives as former addicts while learning to embrace a world that is substance-free soon transforms into a nightmarish scenario of individuals derailed by blackmail, bitterness, and murder. From the easy camaraderie of the group when they get together after the Monday meetings at the pub up at Muswell Hill, the girls--Caroline, Heather and Diana--hide their deepest, darkest motivations. So does Robin, who has a penchant for escorts and suspects that his wife will send a letter to the General Medical Council and, in a heartbeat, have him struck off the register.

As to the real-time world of the ne’er-do-well Chris and his desperate life on the streets, it’s not surprising that he is drawn to Heather as both are addictive personalities. When Heather oversteps boundaries and abuses Tony’s accessibility, Tony finds himself sexually drawn to this manipulative and emotional young girl. Tony might have built a solid reputation and live a comfortable, moneyed life, yet he’s constantly hijacked on the domestic front by dope-smoking daughter Emma and his distant wife, Nina. Something about Heather seriously rattles Nina, especially the sight of her standing on their doorstep begging and pleading with her husband for attention.

Tough-minded and thorough Detective Inspector Nicola Tanner gets a call from Belgravia’s Homicide Command. The case is a routine handover: “one for the bug squad.” There are signs of struggle, blood and broken glass. Perhaps the killer was a disgruntled buyer or a user already high and looking to steal. Tanner and her partner, DC Dipak Chall, face the routine problems that go with the death of someone who lived in isolation--a friend or a furious lover, perhaps an acquaintance or stranger welcomed in. Tanner suspects that, however unlikely, the murder is connected to De Silva’s Monday night rehab group.

Dividing his narrative up into chapters titled “Then and Now,” Billingham’s carefully builds drama in to Tanner’s compelling case that someone in the rehab group is a murderer. From the victim’s obvious screams and struggles to that “terrible realization” of death, Tanner is driven by the words she’s seen in rehab centers and halfway houses across London: the uplifting slogans on the victim’s kitchen wall, “we are only as sick as our secrets.” In an investigation that steadily gets more complicated, Nicola is positive the killing is drug-related.

This is a story of suffering and of secrets, of anger, and of “feeling unworthy.” On orders from Tony, the group join together in their quest for confidentiality, refusing to confide in Tanner. Whether in Tony’s conservatory or around the table in the Red Lion Pub, “what is said among the group can’t go any further.” The group members are easy to hate: conceited, passive-aggressive Alan; snotty Diana with her designer clothes and expensive hairstyle; recalcitrant, moody Chris, always in danger of falling off the wagon; Caroline and her efforts to walk off a little bit of the envy (“as she feels it begin to disperse in her chest step by agonizing step”); and Heather, a young woman who has finally made a choice to get clean and to reclaim her life: “It's what talking about these things does for you. It’s about owning your shame.”

Injecting carefully plotted layers of suspense, Billingham throws us into the spinning jigsaw pieces of each character’s mind: a slice of an addict’s life, a shakily traced killing, and Tanner’s initial frustration then resignation that she can’t get a handle on the twisted identity of the perpetrator. Amid the impenetrable veil of confessions and shameful secrets, a tortured killer succeeds in manipulating and plotting, eventually seeking revenge for their warped and distorted gratifications.