As she established in her erotic thriller, In the Cut, Susanna Moore is not afraid of dark places. Her style is a kind of haute sensationalism; taut, perfectly pitched sentences coupled with an uncanny eye for the goriest detail, the most telling, most unbearable fact. The big girls of Moore’s so-named fifth novel are the women incarcerated in Sloatsburg Correctional Institution, a fictional federal prison located an hour by train from Manhattan up the Hudson River. Some of these women are mentally ill, chronically violent or so unsocialized that prison is actually a civilizing, even humanizing influence. Some are in for frightful crimes — trying to saw off an adulterous husband’s legs with an electric knife, killing a son after wrestling him for a kitchen knife. One woman was high on drugs and driving the car when her husband and child were killed. Another, 17 years old, hid her premature baby son in the closet, where a falling ice skate killed him. A schoolteacher is serving four years for seducing her 13-year-old student (whom she plans to marry upon her release). A repeat offender intentionally had herself arrested by planting two grams of cocaine in her purse, so she could have her baby off the streets with some medical care.

Before finishing this book, Moore volunteered as a creative-writing instructor in a federal women’s prison in Brooklyn, so many details have the sting of close observation. Moore has also read extensively in the literature of incarceration, and appropriated freely, which explains why so many crimes committed by Sloatsburg’s residents seem familiar from old headlines. Years ago I had heard a Los Angeles lawyer tell about the man who kept a prostitute’s head in his freezer, and how his girlfriend would arrange the head’s hair and reapply its makeup so the killer could masturbate with it. In The Big Girls, Moore’s prison psychiatrist claims the complicit girlfriend as a patient.

The novel unfolds through four alternating first-person narrators: a prisoner, a psychiatrist, a corrections officer and a movie star. The blurring of boundaries — professional, emotional, sexual, social — is a thematic drumbeat throughout the novel. Helen Nash, after a lifetime of sexual abuse, has committed an act of filicide that has made her a national celebrity. Her psyche has split into multiple personalities, and her hallucinations are so severe they are usually accompanied by convulsions and vomiting. Having been in and out of mental hospitals for years before her crime, she is a failure of the mental-health system whose doctors routinely sent her back to her abuser. When she is relatively stabilized, Helen measures everything around her, and records her measurements in a notebook (a dollar bill, should you wonder, is two-and-a-half inches by six inches).

Her psychiatrist, Dr. Louise Forrester, is the new head of psychiatry at Sloatsburg. Well off, educated, with a relatively calm childhood in her past, she has her own history of mental illness, having been locked down in Payne Whitney during a manic episode after the birth of her son Ransom. She still relies on a psychopharmaceutical cocktail (self-adjusted) and, against regulations, keeps a flask of vodka in her desk. Another Sloatsburg psychiatrist makes Forrester a laminated card stating that she is “Unfit to Render an Opinion on Anything Because of Sympathy for Criminals.” A joke, of course — and true. When she is overwhelmed, she “takes a deep breath (and a Klonopin)” and reminds herself that she is not an inmate.

Louise’s humanity — her ability to care for and empathize with patients — will prove both salvific and fatal to Helen. A brittle, tentative person — “ladylike and spooked” — Louise muses that she should take lessons from a seductive inmate in the art of talking to men. Louise warms to, and starts sleeping with, her colleague, and co-narrator, Captain Ike Bradshaw. Bradshaw, famous for his sighs, was a police detective who, after being shot (by his wife, accidentally), retired, then returned to work as a prison guard. He is the most grounded, the most psychologically integrated character, the only one to balance compassion, authority and humor, and thus is the emotional heart of the novel.

“We are sisters,” Helen writes to Angie Mills, a vapid young L.A. movie star who is improbably connected to both Helen and Louise. Angie is initially a nasty little cartoon of Hollywood femininity, nattering on about working out, shoplifting and her “whole chemical routine” involving Vicodin, Tussionex and Dalmane: “A little Dexedrine, a platinum AmEx, and voila you get speed shopping, one of my most favorite things in the world.” Moore’s irony is clear; here is a woman whose drug consumption, were she less protected by an ethics-free doctor and celebrity, could make her a big girl fast. Indeed, Angie’s secret husband (she can’t afford the image-degrading revelations of a divorce) is in prison in Arizona for allowing the truckload of Mexicans he was transporting across the border to die in the heat. To Moore’s credit, Angie matures enough as a character to be the only clear head in the heated family tangle around an alleged molestation.

The novel’s central coincidence — Angie in California is corresponding with Louise’s patient and sleeping with Louise’s ex-husband — is Dickensian and implausible, an obvious construct. But plot is not the strongest part of this compulsively readable book. Nor, really, are the torn-from-the-headlines characters. What makes this book so admirable is Moore’s layered and knowing depiction of prison life, a system in disgraceful disarray. The guards are largely inexperienced and often unprofessional — one is a speed freak, one sleeps with prisoners, another has a sore neck “from years of looking the other way.” The medical doctors on call are not available. The mental-health staff are drawn mostly from the dregs of the profession. That said, life around and among the violent, impulse-impaired, mentally ill and unsocialized remains lively. Inmates find every corner, every gap in surveillance to kiss, do drugs, stab each other. The big girls pair off in couples, join families complete with grandparents, sisters, brothers, cousins. “Brothers and sisters fall in love and have sex, not necessarily in that order, and the incest breaks up the family,” observes Helen. “It’s a way to feel safe, despite all the fights. It’s also a good way to make time fly.”

They also develop a wicked dark sense of humor. (The elderly black woman “in prison for killing her middle-aged son in a struggle over a kitchen knife” gets along so well with the prison staff that she is nicknamed Clarisse Thomas “after the Supreme Court justice.”) Fights and any expression of fury or self-righteousness earn peals of delighted laughter from the women. In one group session after a fight in the yard, Louise’s patients start acting out — there’s yelling, an attack, one woman starts vomiting, an overweight older woman in terror drags the psychiatrist to the floor. “I lay there, staring at the dirty ceiling, Mary’s hideous legs under me, as I tried to get my breath,” Louise says. “I began to giggle. I felt like a young girl. The others began to laugh, too. We were soon screaming with laughter. Jackie-O helped me to my feet, and we both lifted Mary into a chair. Weak with happiness, I sent them back to their cells.”

Part potent, darkly funny meditation on mother love, part well-researched exposé of a penal system in grievous disrepair, The Big Girls is a lurid beauty of a book.

The Big Girls | By SUSANNA MOORE | Alfred A. Knopf | 256 pages | $24 hardcover

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