Marla Grayson is a Massachusetts scammer who makes a living by convincing the legal system to grant her guardianship over elders she pretends cannot take care of themselves. She places them in an assisted living facility, where they are sedated and lose contact with the outside world. She then sells off their homes and assets, pocketing the proceeds. She and the court deny a man, Mr. Feldstrom, access to his mother after he attempts to force his way in to the assisted living facility. He later threatens her outside the courthouse, saying that he hopes she is murdered.Dr. Karen Amos informs Marla about a wealthy retiree they can exploit, Jennifer Peterson. A judge appoints Marla guardian after she and Dr. Amos falsely testify that Jennifer suffers from dementia and confusion. Marla moves Jennifer into assisted living and immediately gets to work selling Jennifer's furniture, car and home. While rooting through Jennifer's possessions, Marla discovers the key to a safe deposit box containing a watch, gold bars, bank notes and hidden diamonds, which she takes and stashes away.As Marla's girlfriend and business partner, Fran, helps renovate the house, a man driving a cab arrives and claims that he is there to pick up Jennifer. Fran informs him that Jennifer has moved. He returns to his employer, Roman Lunyov, greatly distressed, who threatens him with a gun. Roman, a crime lord, is Jennifer's son. He orders his underling Alexi to investigate his mother's living situation. Mafia lawyer Dean Ericson offers to pay Marla $150,000 in cash to release Jennifer but she refuses. He threatens Marla and takes her to court. The judge dismisses the case as he cannot prove Jennifer hired him.Fran discovers "Jennifer Peterson" is an identity stolen from a girl who died of polio. When Jennifer refuses to tell Marla her real identity, Marla teams up with Property manager Sam Rice, to have many of Jennifer's basic needs withdrawn. Roman, finding his mother's safe deposit box rifled, sends three thugs to Jennifer's facility to take her. This violent effort fails and Marla helps police apprehend one of the men, Alexi. Fran's police contact informs them that Alexi is the sibling of two other mafia bosses who supposedly died in a fire. Having failed to rescue his mother, Roman has Dr. Amos killed at her office. After hearing the news, Marla and Fran move into one of the unsold properties belonging to one of Marla's previous victims. At the facility, Marla deliberately mocks and insults Jennifer, telling her she will die alone in a few years, and Jennifer, provoked, attacks Marla. Marla distorts the situation at court to convince Judge Lomax to move her to a psychiatric facility.Marla is kidnapped while Fran is attacked in their home. Marla is brought before Roman Lunyov, where she asks for $10 million for Jennifer's release. Roman is impressed by her audacity, but refuses her request. His associates knock her out with chloroform and send her in a car into a lake. She escapes and returns home to find Fran unconscious and badly bruised as gas fills the house. They narrowly escape an explosion and flee to another unsold property, where Marla shows Fran diamonds she has hidden there. She offers Fran a choice: they can use the diamonds to leave right away and start a new life elsewhere or they can get revenge.They track down Roman through his license plate number and kidnap him. They drug him, steal his car, take him into the wilderness, leave him nude on a trail, and burn his car. Roman is discovered by a jogger. Unable to establish his identity, a judge designates him a "John Doe" and appoints Marla as his legal guardian. Marla visits Roman and offers to release him and Jennifer from her guardianship for $10 million. Instead, Roman offers her a partnership in a global business based on her scam. She accepts and, using his money and connections, quickly becomes a powerful, extremely wealthy CEO. Roman is reunited with Jennifer, while Marla marries Fran.While leaving a TV interview about her success, Marla is shot by Mr. Feldstrom, who tearfully reports that his mother died alone in the assisted living facility because no one would let him see her. As Fran cries out for help and Mr. Feldstrom is arrested, Marla dies in her arms.