In her latest novel, Walker combines the narcissistic personality with the end product of a daughter’s twisted betrayal. The story is less about Emma, the missing girl of the title, than about the broken-down family that forms the story’s core. Walker is at the top of her game as she unfolds the mysterious musings of a girl who dissects everything in her life and then fights back against her relentlessly controlling mother. After disappearing three years ago with her sister Emma, Cass Tanner has unexpectedly returned home. Dr. Abigail Winter, chief FBI psychologist, and Special Agent Leo Strauss--the officers originally assigned to investigate_-are shocked at Cass’s sudden reappearance. Abby in particular has not forgotten the Tanner sisters; their loss has lain dormant in the shadowy corners of her mind.

At the time, everyone agreed that the case was maddening. The girls’ mother, Judy Martin, describes the fight the night before, the shrill screaming and the girls crying. Abby had to have counseling to reconcile her frustration, anger and disappointment over the outcome of the search. Everything was in play: the car at the beach and the girls’ shoes left by the shore. Nothing suggested that the girls had ever planned to run away together. The forensic evidence came back clean, except for a broken picture frame which Judy said resulted from the girls' fight over a necklace, a flying-angel medallion on a silver chain.

But now Cass is back, and Emma is still missing. With Cass ready to talk, Abby and Strauss are summoned back to the Martin home, where Cass shepherds attention from Judy and her stepfather, Jonathan. In these early scenes, Cass is largely a reliable narrator. She talks about the months that led up to her vanishing, a dramatic critique of self-obsessed Judy, free-spirited Emma and the girls’ privileged lives spent in prestigious private schools and expensive European summer camps. Cass tells us her mother can change, chameleon-like, when it suits her, especially after her divorce from the girls’ father, Owen Tanner. Judy’s animosity toward her daughters increased after they asked to live with Owen and their half-brother, Witt. This anger eventually threatened to spiral out of control with the arrival of Jonathan and his son, Hunter, who from the start was obsessed with Emma.

Abby cannot see Cass’s confession through the same lens, “the one she was telling and the one she wasn’t.” She still can’t figure out what drove the girls to leave. As Cass unfurls her strange, detailed tale about a Maine Island inhabited by Bill and Lucy Pratt and and a local boatman named Rick, Abby tries to stitch together Cass’s fractured self from a sophisticated tale far beyond Cass’s years. Abby applies her research on narcissistic personality disorder to the mystery behind the necklace, which she’s convinced is somehow involved in the girls’ disappearance.

Time bends and twists as Walker moves us through Cass and Abby’s dueling narrative to an emerging portrait of dark-haired Emma, who traipses through the Martin house in short skirts and a tight sweater, beautiful, severe, tortured, and ruthless: “someday it will be just the two of us.” According to Cass, Emma always made light of things; nothing Judy said could touch her. What if Emma had not escaped? What if the things Cass knows are just the tip of the iceberg? But Emma also kept secrets “like ammunition.” While Cass treated Emma like an authority figure (“like a mother”), she also told stories--warnings and lessons about who Judy was and what she was capable of doing, this narcissist who changes her background story to match her audience.

“I missed her like a miss my own heart. I wanted Emma, I wanted revenge justice,” says Cass as Abby begins to figure out the truth behind Emma’s whereabouts and how people like Judy are masterful in their deception and relentless in their manipulation. However strong the façade of Judy’s life appears, a crack in her foundation threatens to demolish her wellbeing. Why is Judy plagued with guilt? What secret is Jonathan hiding? What about Lisa Jennings, the school counselor, interviewed extensively three years ago, who talked to Emma that fall? No one wants to talk about it except for Cass, who confides to Abby about the night Judy attacked Emma while she slept, cruelly cutting off her hair with a pair of scissors.

As Abby and Cass navigate through the darkly suspenseful aftermath of their suppressed memories, Walker finally gets to the over-the-top "aha moment” of Emma’s whereabouts and Judy’s meltdown, when she spews with all the anger of a hurt child. Cass finally attempts to move forward, reinventing herself far from the selfish machinations of a mother who desperately tries to make everyone love her by using the only weapons she knows: cruelty and fear.