Kristen Arnett’s new novel, “With Teeth,” is the perfect baby shower gift for someone you hate.

Absolutely captivating and scathingly frank, it’s a story of motherhood stripped of every ribbon of sentimentality. Arnett conjures up the disturbing mixture of devotion and alienation endured by anyone raising a child they don’t understand, don’t even like. And at its heart, “With Teeth” explores the way parenthood exacerbates our own vulnerabilities and delusions.

The novel opens in Orlando, with a moment of ordinary tedium and extraordinary terror: Sammie leaves her son, Samson, alone on the swing for just a moment while she throws away his half-eaten lunch. When she turns back around, a man is walking out of the playground holding Samson’s hand. She runs, she jumps a fence, she screams, but no one seems to hear her — not even her son. “Samson just stood there beside him,” Arnett writes. “She could see the man’s lips moving, but she couldn’t make out any of the words. Her son, quiet all day every day, looked up at the man and smiled. Actually smiled. Full-on toothy grin.”

That smile hurts because the boy never smiles at Sammie. Indeed, her only reward for saving her son from abduction is his irritation. “Samson never spoke unless he absolutely had to,” Arnett writes. His behavior would seem to place him somewhere on the autism spectrum, but the doctor, his teachers, everyone assures Sammie that Samson is “a perfectly capable, fully functioning fourth grader who just needed an attitude adjustment.” That’s easy for them to say; they’re not taking care of him full-time. They don’t see him pouring paint all over the living room or chasing a cat off the balcony.

“How often had she looked at Samson’s blank stare and wondered if something worse was lurking underneath?” Arnett writes. “Sammie was left to wonder alone about the way her son’s eyes seemed to roll over black with internal rage, like a shark’s.”

Speaking of sharks, the novel’s title stems from an early scene when Samson starts acting up on the way to the therapist’s office. Trying to restrain him, Sammie reaches over and grabs his wrist. He bites her. “Before she realized what she was doing, she leaned down and took a bite of his own arm — sank her teeth into the meaty place directly behind his wrist. She wedged them in, deep, and then they were both looking at each other, engaged in some terrible battle to see who’d be the first to let go.” It’s a shocking moment, comic and grotesque and, yes, wholly understandable — like everything in this novel about the pain of motherhood, the actual scars left on the skin and the soul.

If there’s a spike of horror running through “With Teeth,” it’s the turn of the screw that drives into an exhausted parent’s brain. But those common pressures are exacerbated for Sammie by the extra burden of having to prove that a gay couple can do “the family thing” right. Her wife, Monika, “wanted them to be normal,” Arnett writes. “She was always eager to impress with their ‘normalcy.’ . . . Two perfect gay moms and their handsome, grinning son.” It’s an illusion that leaves Sammie no room to relax. “People were already judging them,” she thinks, “sure that a boy with two mothers wouldn’t turn out right.”

Maintaining that facade exacts an increasingly enervating effect on Sammie. Once a successful manager, she’s been reduced — I mean, elevated — to the blessed role of stay-at-home mother. While her spouse continues with a demanding, interesting law career, Sammie must switch to part-time remote work. “She could do it all — copyediting, client emailing — in her sleep,” Arnett writes, “and sometimes that’s exactly how she felt: like she was sleepwalking through her work and her life.”

Arnett’s sympathetic attention to the cascading flow of Sammie’s depression is heartbreaking. But between every chapter, the novel offers one-page moments, each from a different minor character’s point of view. It’s just a fleeting switch in perspective, easy to discount, but oddly base-shifting if you pay attention. Again and again, we’re reminded that Sammie’s hermetically sealed understanding of her dismal situation is not necessarily complete — or even correct.

As Samson’s birth mother, she feels as though she never got her body back. She’s awkwardly suspended between her previous life as a desirable queer woman and her new role in a suffocating simulacrum of domestic happiness. While Monika remains charming and gorgeous, Sammie remembers sex like some foreign country she’ll never again visit. In one of the novel’s most poignant episodes, she starts sneaking into a neighbor’s yard at night and peering in the window for moments of respite. “She was just making sure that this other woman — her mirror, her Alice in the looking glass — was succeeding. Just seeing a woman like her doing well gave Sammie a sense of satisfaction. Of hope.” That’s the way hope usually comes in “With Teeth”: glazed with despair.

Divided into the four seasons but moving through many years, this strangely shrewd and tender story follows Sammie and Samson as they both mature and continue negotiating with each other. Their relationship evolves, but Sammie always finds her son baffling. At her lowest moment, she thinks back to that strange man in the playground parking lot and wonders “how her life would have changed if he’d succeeded. If she’d just let him take her son.”

Arnett is that rare, brave writer willing to articulate the darkest thoughts even the best parents entertain while trudging along through the most challenging job in the world.

“What a weird thing,” Sammie thinks, “to love another human.”

Ron Charles writes about books for The Washington Post and hosts TotallyHipVideoBookReview.com.

With Teeth

By Kristen Arnett

Riverhead. 290 pp. $27