Marla Grayson, portrayed by Rosamund Pike, is a cunning con artist who cleverly manipulates the legal system to secure guardianship over elderly individuals whom she deceitfully claims are incapable of caring for themselves. Under her watch, these vulnerable individuals are placed in an assisted living facility, where they are sedated and cut off from the outside world. This allows Marla to liquidate their homes and assets for her personal gain.
In one particularly unsettling incident, Marla denies access to a distressed man named Mr. Feldstrom, played by Macon Blair, who desperately tries to see his mother. During a courtroom battle, Marla defends her actions by asserting her role as a professional caretaker, even going so far as to claim that her actions ultimately protect the elders from their greedy offspring. Following this encounter, Mr. Feldstrom angrily threatens her, wishing death upon her.
Meanwhile, Dr. Karen Amos, portrayed by Alicia Witt, tips Marla off about a wealthy retiree named Jennifer Peterson, played by Dianne Wiest, who appears to have no close family. Excited by the opportunity, Marla, alongside her business partner Fran, steps up her game, conducting extensive surveillance on Jennifer. They discover that not only does Jennifer own a valuable home, but she also has greater financial resources than initially thought, including multiple bank accounts generating significant interest.
Using falsified testimonies claiming that Jennifer is suffering from dementia, Marla is appointed as her legal guardian. In a calculated move, she swiftly relocates Jennifer to an assisted living facility, confiscating her phone in the process, while starting to auction off Jennifer's possessions, including her furniture, car, and home. As she rummages through Jennifer's belongings, Marla stumbles upon a safe deposit box containing a treasure trove of valuables—watches, gold bars, and hidden diamonds—which she decides to keep for herself.
As Fran, portrayed by Eiza González, supports Marla in renovating Jennifer's house for sale, an unexpected visitor named Alexi Ignatyev, played by Nicholas Logan, shows up. He claims to be there for Jennifer, but Fran informs him of Jennifer's recent move. Alarmed, Alexi returns to his employer, Roman Lunyov, played by Peter Dinklage, who turns out to be Jennifer's son and a crime lord. Roman's frustration boils over, leading him to threaten Alexi and demand an investigation into Jennifer's situation.
In a shocking turn, a mafia lawyer named Dean Ericson, played by Chris Messina, offers Marla a staggering $150,000 in cash for Jennifer's release, but Marla dismisses this, insisting her price is a whopping $5 million. After the case is dismissed in court due to insufficient evidence from Dean, the story takes darker twists. Fran uncovers that "Jennifer Peterson" is actually an identity stolen from an infant who met an untimely demise, which only escalates the peril surrounding them.
Marla teams up with property manager Sam Rice, portrayed by Damian Young, to deprive Jennifer of her essential needs as Roman's frustration grows. When Roman discovers that his mother’s assets have been exploited, he sends a group of thugs to retrieve her; this violent attempt fails, leading to one thug, Alexi, being apprehended by the police thanks to Marla’s intervention.
However, the stakes elevate significantly when Roman orders the assassination of Dr. Amos and unleashes chaos on Marla and Fran, leading to a series of tense encounters, including Marla being kidnapped and escaping from a watery grave. After enduring harrowing experiences, Marla and Fran muster their strength to chase vengeance against Roman. They hatch a plan to abduct him, drug him, and leave him in a vulnerable state to be discovered in a forest.
Their brilliant plan results in Roman being declared a "John Doe," leading to Marla's guardianship over him. In a twisted exchange, Marla offers to release both Roman and Jennifer for a substantial $10 million; Roman proposes an unexpected partnership instead, leveraging his criminal enterprises to propel Marla into significant wealth and influence.
In the end, while Marla ascends to a life of power post-transaction and marries Fran, tragedy strikes as revenge catches up with her. A shot from Mr. Feldstrom, who mourns his mother’s demise due to Marla’s machinations, pierces through her newfound success, leaving Fran to witness the shocking climax of Marla's rise and fall.
