Behind These Four Walls

The novel opens with an unnamed man driving into the desert east of Los Angeles. Matthew Leonard, an accountant, has been blackmailed into choosing between two fabricated scandals: accept blame for embezzlement he did not commit, or allow compromising photos of an affair to reach his wife, Maia, who recently gave birth. He texts his blackmailer agreeing to take the fall, texts Maia an apology, and kills himself.

Six months later, 26-year-old Isla Thorne engineers a chance encounter with Holland Corrigan, the 19-year-old collegiate fencer and daughter of billionaire Victor Corrigan, chairman of the Corrigan Group, a global conglomerate. Isla approaches Holland in a parking lot, points out a flat tire she caused, deliberately breaks Holland's phone, and arranges a rideshare, knowing Holland will invite her along. At the estate, Holland's eldest brother Myles Corrigan pays Isla for her help. The encounter is a calculated setup: Isla pickpocketed Holland's keys and student ID to infiltrate the family.

A flashback explains Isla's motivation. In Los Angeles, Isla and her partners Rey, a tech specialist, and Natalie "Nat" Wang, an aspiring actress, run a side business finding compromising information for public relations firms' clients. Isla delivers evidence of Leonard's affair to a firm whose client is the Corrigan Group. After Leonard's suicide, Rey discovers the embezzlement was planted and the affair was a honey trap orchestrated from Virginia. The trio realizes they were unwitting tools in Leonard's destruction. The case reawakens Isla's guilt over her best friend Eden Galloway, who vanished ten years earlier in Charlottesville, Virginia, after telling Isla she had "unfinished business" with the Corrigans. Isla decides to infiltrate the family, with Rey and Nat supporting her remotely.

Back in the present, Isla returns Holland's keys and ingratiates herself with the family. She meets Victor; his right-hand man Dixon; Brooke Corrigan, Victor's wife, who is immediately hostile; and Jackson Russell, the family foundation's lawyer. At dinner, Holland mentions someone named "Edie," and the room goes cold.

That night, Isla sneaks into Victor's study and finds a photograph of a younger Eden with Victor, Eden's bracelet, and a letter postmarked from Daytona weeks after Isla and Eden left that city. The letter disowns the Corrigan family. Isla realizes Eden Galloway was Edie Corrigan, Victor's illegitimate daughter by his former assistant Elise, and that Eden hid her true identity throughout their friendship. The bracelet's presence and the letter's suspicious timing suggest Eden may not be alive.

Interspersed flashbacks reveal that Isla and Eden met in Daytona when Isla was a ward of the state and Eden was caring for her dying mother, Elise. After Elise's death, Eden took her mother's gold locket chain and insisted on stopping in Charlottesville. She left their motel room one night and never returned.

Isla secures a position on the estate by convincing Victor to let her write a profile for his upcoming Man of the Year award. She interviews townspeople and learns Eden attended public high school, loved theater, and changed dramatically after a car accident one Labor Day weekend that was barely covered in the press. She visits James Mitchell, a friend of Victor's younger son Bennett Corrigan. James was secretly in love with Eden and is guilt-ridden but stops short of confessing.

In Eden's preserved bedroom, Isla finds a hidden note in which Eden writes she would rather leave than have her father see her as a monster. When Victor catches Isla in the room, Brooke seizes the moment by suggesting Isla make a peace-offering drink while ensuring a bottle of almond liqueur is placed at the bar. Victor, severely allergic to almonds, has a dangerous reaction; Dixon saves him with an EpiPen. Staff reveal Brooke used the same tactic years earlier to frame Eden for harming Holland, who is also allergic, destroying Victor's trust in Eden and driving her away.

The investigation escalates. With Detective Tolson Bowen, a local officer Isla recognizes from ten years earlier, she finds a brief article about the fatal mountain-road accident. During a hunting trip on the estate, an unknown shooter pursues Isla through the woods. Myles finds her and identifies three sets of tracks, suggesting someone intervened to protect her.

James contacts Isla and drives her to the old Abbott farm, confessing along the way. Thirteen years ago, Bennett drove drunk and turned off the Jeep's headlights on a dark mountain road, then blinded an oncoming minivan with high beams, killing a family of four. Their parents covered it up. When Eden returned three years later demanding the truth, Danny Crawford, Bennett's associate, pushed her into broken glass at the barn, impaling her side. She fled and was never found. Someone sets the barn ablaze; Isla and James escape, but James pursues Danny's truck down the mountain. The vehicles collide, killing Danny and critically injuring James.

Isla sends evidence that Bennett and Danny framed Leonard to his widow, who goes public. Victor suspends Bennett but shields the company by not naming him.

Breaking into Jackson's home, Isla cracks his wall safe and finds an unsigned will naming Bennett as sole heir and a voice recorder containing Eden's narration of her final night. When Jackson returns with Brooke, Isla overhears them confirm their long-running affair, that Bennett is Jackson's biological son, and their plan to install Bennett as chief executive officer and take over the Corrigan Group.

Isla's cover is blown when Brooke brings Charli Galveston, the woman who sheltered teenage Isla in Atlanta, to the estate. Charli reveals Isla's true identity and connection to Eden, and Victor orders her to leave. Myles drives Isla to her motel, where she plays him Eden's recording. On it, Eden narrates fleeing the barn wounded, reaching a back road, and encountering a figure she recognizes who, instead of helping, removes the glass shard from her wound, killing her. Myles agrees to help expose the truth at Victor's reception.

At a storage facility in Ruckersville, Isla discovers a yellow Jeep belonging to Roger Monroe, one of Bennett's friends, hidden by Jackson as leverage.

At the Man of the Year reception, Isla plays Eden's recording for the family. Bennett denies everything while Brooke and Jackson slip away. Using tracking devices Myles planted, Isla follows them to a clearing where Jackson confesses: He found Eden dying on the road, removed the glass to ensure her death, buried her, forged the disowning letter, and hid the Jeep. He tells Bennett that Victor is not his biological father. Isla emerges from the trees with Victor, Myles, Dixon, and Lawrence, the head groundskeeper. Victor shoots Jackson in the shoulder before being restrained. Eden's remains are exhumed, identified by Elise's gold locket chain. Jackson escapes in the chaos.

Hours later, Jackson infiltrates the mansion and holds Isla and Victor at gunpoint, demanding Victor sign the forged will. Isla strikes Jackson's wound with a jagged rock she has carried since the hunting trip. Myles and Lawrence burst in, and Isla drives Holland's fencing saber through Jackson's hand, subduing him.

In the aftermath, Bennett faces being cut from the family, Brooke faces divorce, and Victor is expected to step down. Myles and Isla agree to build a genuine relationship. Isla sits at Eden's grave near the estate's solarium, marked with a plaque reading "THE GARDEN OF EDEN." She reflects that in finding Eden and securing justice, she accomplished what she could not for her own father: She found the truth and brought her best friend home.