The possibility of finally awakening the nightmares of the past proves to be an impossible choice for anxious Fern, who lives in Boston with Eric, her husband. The catalyst for Fern's descent into unreality is red-headed Astrid Sullivan, reported missing ten day ago by her wife, Rita Diaz. The timing of her disappearance--almost exactly 20 years since her abduction from a small New Hampshire town in 2000--coincides with Fern's memories of Astrid Sullivan's original abductor, who was never caught.

Feeding into a sense of paranoia and shaping a tragic accident into something far darker, Collins molds her themes of isolation and the innate desire to find something pure in Fern, who is battered by her past. Fern is convinced she actually knows Astrid, though at the time of Astrid's abduction she was only 12 years old. Reminding her of all the girls who just disappear, Fern thinks of kidnappers with masks and how everyone was obsessed with the story, especially since her reappearance was so weird. Fern dreams of Astrid because she saw her on television. Her thoughts seem to be constantly tangled up with her.

Astrid's second disappearance coincides with her new memoir, . With a recent spike in sales, the book has zoomed up the bestseller lists. Readers are speculating that it was the book's publication that drew Astrid's original kidnapper out of hiding. Astrid's memoir belongs on Fern's long list of triggers. She's certain that she knows Astrid: "I've met her, But when and where?" Fern is obsessed with finding Astrid and unlocking the secret that lies behind the red door, perhaps the basement where her first kidnapper kept her. There were never any witnesses to Astrid's kidnapping--that is until Fern thinks she had a role in it.

Collins casts her story in furtive layers of suspicion and abandonment as frail, damaged Fern is overwhelmed by memories of Astrid, the basement, and a secret hidden away. She recalls hands, empty then beseeching, "open as wide as a mouth gasping for air." As the itch on her wrist flares, Fern recalls how Astrid was asking, almost begging for help. As Fern reads excerpts from the prologue to Behind the Red Door, Astrid becomes a sort of imagined girl: "that I'd invented her as a way to cope with the trauma, a way to find some hope to hold on to while I endured my basement nightmare." Perhaps Astrid is someone else, a ghost of her former self, "a girl I still believed should be spared." The news story lies like a transparency over Fern's usual nightmare, fanning the flames of her anxiety.

Tension soaks the novel, shimmering as Fern's father and mother, attempt to withhold small facts and bend truths while letting the events of Fern's past become blurred. Ted's psychological experiments on Fern are startling, intrusive and cruel. She constantly hears Eric's voice telling her that her father doesn't care about her, "not the way a parent should." The subject of Ted's research project, Fern questions Ted over why he never seemed to love her enough. Disquiet turns Fern's heart to a fist. If the kidnapper is repeating his exact same patterns from 20 years ago, then soon he'll be coming after Fern.

Recollections are powerful: her mother's art studio, where the cracks in her marriage first started to show; the woods outside Fern's childhood home; the flashes of Astrid, her two-dimensional face on a poster; and the voice of Astrid herself, raised in a strict Catholic household that vacillated between guilt and rebellion. The details of Astrid's past were previously undisclosed, though it's common knowledge there was a witness to what happened - a young girl who never came forward, just one of the "girls who see girls disappear, girls who never speak up." Father Murphy once viewed Astrid as filthy and unholy, an abomination, while Ted is "what you get"--his arrogance, his manic energy, and his intolerance of distractions. There's also the figure of a man, a creature with no skin and no head but wearing a welder's mask. Perhaps he really was a man, not just a monster from a nightmare. From the confusion and dredged-up memories to the whispering woods that cast "knife-sharp shadows," Fern is determined to fight through all of it for Astrid, who might be back in a basement she thought she escaped.

Oscillating between the hopeful and the sad, Collins captures Fern's dissolving memories: "I can't see her in front of me anymore, can't hear her either." Collins' novel is sinister, highlighting the variances of intent and reality in chapters that move between the past and the present, revealing the ultimate keeper of secrets and the barriers that must be weakened in order for Fern to discover the truth behind her connection to Astrid.