Though a bit overwrought, especially in the final sections, Perks' novel set in contemporary Dorset adds a new twist to the "missing child" narrative. Charlotte is only too happy to take Harriet's daughter Alice to the local fair. A recent arrival in the quant village of the village of Chiddenford, Charlotte is lucky to have formed such a tight bond with Harriet; she also admires her for the connection she has with her children. Despite Alice being four, Harriet has never left her daughter with anyone before. Charlotte is eager to watch Alice, though both women are a little more on edge than usual since a boy was taken last October on the other side of Dorset.

Having survived fifteen years of a disastrous marriage, Charlotte may have gotten too comfortable with the easy flow of her life. She faces another trauma when Alice goes missing. Momentarily distracted by her technology, Charlotte recalls seeing her own kids, Evie and Jack, laughing on the Jungle Run as Jack hauls over the edge. The fallout from Alice vanishing ricochets throughout Harriet and Brian's increasingly tenuous marriage. The news spreads rapidly--a whisper that passes through the crowd, kicking up a burst of activity. Faced with an increasing threat of danger, everyone has a role in finding her.

Charlotte knows there's only one person whose fault this was. She admits to Detective Angela Shaw that she lost herself in texts and Facebook and maybe looked up occasionally but not often enough to spot Alice. Harriet gulps back a sob. Brian decides to lay the blame squarely at Charlotte. Where was she when all this happened? Harriet can almost feel his rising panic, the thought of a mother not watching a child. It's something that obviously fills Brian with dread. Brian becomes a fearful presence, a cruel bully who is openly misogynistic, unafraid to wield his power over Harriet, who flashes on little Mason, the boy the press describes as having vanished into thin air.

"I wasn't happy after Evie was born and Harriet was a good listener. She's one of my best friends." That quote reflects the dynamic between the two friends, a dynamic essential to the plot. While thoughts of Charlotte and the appeal spin in Harriet's head, spending a night without Alice in the bedroom next to hers gnaws deeply. How can she get through it? How can she function now that Alice is no longer with her? All she can see is Alice's pale and frightened face. Harriet's frustration rips through her "like lightning," jolting her upright and onto her feet, unleashing "a raw and guttural scream."

With its sinister undertones, Perks' story staggers along with its accrued fears of marital dysfunction, especially the insanity of Brian and Harriet's relationship. Her One Mistake evokes the sort of psychological intimidation and cruel mind games men (and sometimes women) can play on themselves and each other. Guilt proves to be destructive. When Harriet isn't thinking of Alice, unwanted thoughts of Charlotte fill her head. Harriet and Brian seem to be clawing at hope, desperate for Charlotte to tell them something that could give them an answer. Alice's disappearance is proof that Charlotte is a careless mother whose children "run feral."

Switching from Charlotte to Harriet's perspective, Perks gives us the space to do a deep-dive into the lives of both women as well as Brian, who becomes evermore demanding and demented as the story progresses. Is Brian a deceptively smooth charmer, a true wolf in sheep's clothing? Or is he a loving, legitimately concerned father? As the past twelve months "flicker like a movie" behind Harriet's eyelids, the realization that Brian created a life that she and Alice can't escape from makes it seem like her plan is a good idea. What would the police, the press and Charlotte see if Harriet could strip back the walls that Brian built so skillfully around them?

Like the calm before a storm, the book never quite gets there. The cliched ending doesn't seem that hard-won or deserved, though Perks is able to fool us over Harriet's true motivations and her ability to see her daughter everywhere in vivid, "Tell-Tale Heart" fashion. Regardless of the whereabouts of Alice, Her One Mistake is never really a missing child mystery but about a couple involved in a sinister power game of betrayal and survival in which poor, naive Charlotte is a pawn in an effort to find the winner.