The Arrangement

The Arrangement (2021) is a psychological thriller by Kiersten Modglin. The novel follows married couple Ainsley and Peter Greenburg, who agree to an unconventional solution to save their failing marriage: dating someone else one night per week. Their arrangement leads to deadly consequences that bind them together in unexpected ways as the story explores themes including Control and Manipulation Disguised as Love, The Erosion of Truth in Intimate Relationships, and The Performance of Domestic Normalcy as Survival.

Modglin is an Amazon Top 10 best-selling author of psychological thrillers and a member of International Thriller Writers, Novelists Inc., and the Alliance of Independent Authors. She is a KDP Select All-Star and a recipient of ThrillerFix’s Best Psychological Thriller Award and Suspense Magazine’s Best Book of 2021 Award. Modglin has written numerous standalone psychological thrillers including The Missing Piece and The Good Neighbors. The Arrangement is the first book in the Arrangement trilogy, followed by The Amendment and The Atonement.

This guide refers to the 2021 Kiersten Modglin edition.

Content Warning: The source material and guide feature depictions of death, graphic violence, antigay bias, emotional abuse, self-harm, disordered eating, and sexual content.

Plot Summary

Ainsley Greenburg, a bank branch manager and mother of three, has grown distant from her husband, Peter Greenburg, an architect, after years of prioritizing work and childcare over their marriage. Feeling their bond deteriorating, Ainsley, who considers herself a “fixer,” proposes an unconventional solution: Each partner will date someone else one night a week using a dating app, with strict rules to prevent emotional involvement and maintain secrecy from their children. Ainsley adopts the pseudonym “Annie Green,” while Peter becomes “Pete Patterson.” Though apprehensive and motivated by fear of losing Ainsley, Peter agrees.

Ainsley selects Stefan De Luca, a widower who works as a police officer, for her first date. For safety, Peter asks her to leave a sealed envelope containing Stefan’s name and their meeting location. Ainsley dines with Stefan, finds him kind but emotionally invested, and feels guilty for using him. She chooses not to pursue sex and returns home late, refusing to disclose details per their rules. Meanwhile, Peter becomes consumed by jealousy, secretly opens Ainsley’s envelope despite their agreement, and finds only a taunting note saying, “Sorry, honey. Rules are rules” (31). The following week, Peter chooses Mallory, a younger woman, for his date. Their evening quickly becomes sexual at her apartment. When Peter returns home, he finds Ainsley more passionate and assertive, suggesting that the arrangement has reignited some physical spark.

Both partners struggle with jealousy and emotional fallout as their arrangement continues. Ainsley feels guilty about potentially hurting others and adds a new rule: Partners must clarify to future dates that they seek only casual sex. Peter faces unexpected complications at work when he matches with Gina, a colleague, on the app. Gina recognizes him and initially suspects that someone is impersonating him, but he admits that the profile is his. Gina expresses interest in meeting, and Peter agrees, breaking a rule by seeing her outside his prescribed day, but he leaves their dinner date early after a call from Ainsley. Complicating matters further, Gina is revealed to be Mallory’s landlord and roommate, leading to a tense encounter when the women discover that Peter pursued connections with both of them around the same time.

Stefan grows increasingly persistent after Ainsley does not reciprocate his interest following their first date and ignores his subsequent messages. He sends her repeated messages and discovers her real name and address. On the night when Peter is out to dinner with Gina, claiming to be working late, Stefan arrives at their rural home. Ainsley, frightened, calls Peter for help. 

When Peter arrives, he finds Stefan armed and behaving aggressively. Fearing for Ainsley’s safety, Peter attacks Stefan with a baseball bat, killing him on their porch. He searches Stefan’s pockets and discovers a police badge, confirming that he was an active police officer, which intensifies their panic. Panicked about potential consequences, Ainsley and Peter decide against contacting authorities. They bury Stefan’s body under their porch. Ainsley drives Stefan’s truck and phone to the airport to eliminate evidence, while Peter meticulously cleans the scene. Ainsley later disposes of the murder weapon in a city dumpster.

The following days bring intense guilt, paranoia, and tension. Ainsley justifies their actions as necessary to “fix” their marriage and protect their family. Peter becomes fixated on erasing all physical evidence while struggling to maintain normalcy for their children.

Illiana De Luca, Stefan’s wife, launches her own investigation and confronts Ainsley at the bank that she manages. Illiana reveals that she knows about Ainsley’s date with Stefan and threatens to involve the police unless Ainsley cooperates. Later, Illiana then visits the Greenburg home, again demanding answers. During her visit, she receives a call that Stefan’s truck has been discovered. When the police begin searching for Stefan and question Ainsley at home, she shows them messages from the app that portray Stefan as obsessive. Shortly after, Illiana goes missing, having left her phone and belongings at home. This temporarily diverts suspicion from the Greenburgs while complicating the police investigation.

The police later provide shocking news: Stefan was a suspected serial rapist, with evidence including trophies and distinctive rope found in his truck. They believe that Illiana was complicit in or aware of his crimes. Officers warn Ainsley and Peter to remain vigilant but no longer view them as suspects. The couple internally grapples with the knowledge that Stefan, whom Ainsley manipulated into coming to their home, may have intended to harm her, further complicating their sense of guilt and relief.

Concurrently, Ainsley’s best friend, Glennon, becomes suspicious of the couple’s behavior. She confronts Peter about his affair with her husband, Seth, and threatens to expose him if he does not confess to Ainsley. Glennon and Seth’s marriage is revealed to be one of convenience, as Seth is gay, and Glennon agreed to the union for financial benefits and mutual support. Following Peter’s affair with Seth, Glennon decides to end her marriage.

In a series of explosive confessions, Peter admits to Ainsley his string of affairs, including with Seth. Ainsley then reveals that she had known about Peter’s infidelities and that the open-marriage arrangement, which was her idea, was no spontaneous act. She also reveals that she intentionally selected Stefan for his position as a police officer and manipulated him into believing that she was abused. Her goal was to provoke Stefan’s intervention and, consequently, Peter’s violent protective response, thereby creating a shared, dark secret to bind their marriage through mutual culpability. Ainsley confesses that while Peter delivered the fatal blows, she considers herself the true architect of Stefan’s death.

Six months later, the Greenburgs demolish their old porch and pour a new concrete patio over the burial site. Their intimacy is revitalized, and their marriage appears outwardly stable. They attend counseling, committed to “total honesty.” 

However, a final layer of deception emerges when Peter secretly visits a hidden lair built into their home’s design. He is revealed to be a serial killer who has murdered numerous women over the years, keeping their trophies in a concealed duffel bag. He also murdered Illiana, unbeknownst to Ainsley, and buried her with Stefan under the new patio. When Peter checks his trophy collection, he discovers that the bag has been emptied except for a sealed envelope bearing Ainsley’s signature, which reads, “Sorry, honey. Rules are rules. No more secrets” (209). This final twist reveals that Ainsley knew about Peter’s darkest secret all along, ensuring that both are bound by mutual knowledge and complicity in a fragile, uneasy alliance.