The Perfect Son, published in 2019, is a domestic thriller novel by the American author Freida McFadden. The novel follows the seemingly idyllic Cass family as they navigate life in suburbia. While Erika Cass appears to have her life together as a dutiful mother and wife, she’s hiding a major secret: She suspects her son Liam is a killer. When a girl in town goes missing after a date with Liam, Erika is forced to consider how dangerous her son really is. The novel explores themes such as The Threat of Inheritance and Genetics, Appearance Versus Reality, and The Safety and Expectations of Families. Notably, this novel’s consideration of mental health conditions relies on harmful and inaccurate stereotypes about correlations between mental health conditions, violence, and genetics.

This guide refers to the independently published 2020 paperback edition of the novel.

Content Warning: The source text includes references to physical assault, psychological manipulation, child abuse, and animal abuse. Additionally, the source material uses offensive terms for mental health conditions throughout, which are replicated in this guide only in direct quotes of the source material.

Plot Summary

Erika Cass lives a seemingly happy life in the New York suburbs. She has a successful husband, Jason, and two children: a moody daughter, Hannah, and a handsome and smart son, Liam. She favors Liam more than Hannah. However, Erika is hiding a dark secret: Liam has disturbing and violent thoughts, and she views it as her mission to protect him from acting on those thoughts. While Liam appears to be a star student, debate team member, and track athlete, he has a dark past. He was kicked out of kindergarten for duct-taping one of his classmates and leaving her in a closet, traumatizing the girl severely.

One day, Hannah teases Liam about his crush, Olivia Mercer, in front of Erika. Determined to protect Olivia from Liam, Erika goes to her son’s debate match to figure out who she is. She sees a girl named Olivia Reynolds and assumes that she is the Olivia on whom Liam has a crush. Erika calls her private investigator, Frank Marino, and asks him to do what he’s done with all of Liam’s previous romantic interests. Frank approaches Olivia Reynolds and threatens to release damning text messages and nude photos if she continues to talk to Liam. She agrees not to continue speaking with him.

However, Liam continues his relationship with his true crush: Olivia Mercer. The two flirt in math class, and he invites her to his debate match. At the match, he asks her out on a date, to which she agrees over the objections of her best friend, Madison Hartman. Madison finds Liam inauthentic, and she’s heard rumors that many boys are scared of him. Regardless, Olivia goes on a date with Liam, falling in love with him after he lends her his jacket when she’s cold.

At the diner, Olivia and Liam flirt, splitting a vanilla milkshake. However, Liam’s best friend, Tyler Martinson, ruins their fun by picking a fight with Liam. Liam de-escalates the fight by scaring Tyler and covertly threatening his family. Olivia’s mother comes to pick her up, ending their date early. Liam is sad to see her go and suggests they hang out again soon.

When Olivia gets home, Tyler is waiting for her on her front steps. He tells her she shouldn’t date Liam because he’s dangerous, but he gives her no specific details for his suspicion. She ends the conversation when he tries to flirt with her. Later that night, Olivia hears someone throwing rocks against her bedroom window and finds Liam below. She goes outside to meet him, and they share a kiss.

That same night, Erika struggles to sleep. Not wanting to wake her husband, Jason, she walks around the house and finds Liam’s room empty. She begins to panic and wakes up Jason, who suggests she call Liam. When she speaks to Liam, he tells her he couldn’t sleep and decided to take a walk. Erika demands he come home immediately and then takes a Xanax to head off an oncoming panic attack. Jason offers to wait up and chastise Liam when he returns home.

The next morning, Liam appears to be in a very good mood, despite both his parents yelling at him. Erika is shocked to find reporters and police at the school when she drops off Hannah and Liam. Hannah discovers on her phone that Olivia Mercer is missing. Erika becomes worried that her disappearance is connected to Liam’s late-night adventure. Her fears are validated when she discovers the Mercers’ home address programmed into her car’s GPS.

When Erika gets home, her mother is waiting for her. Her mother tells her that she’s been keeping a secret from her: Erika’s father, whom she long believed dead, is alive and in prison for first-degree murder for poisoning his lover. Shocked by the news, Erika asks her mother to give her time to process the new information.

Later in the day during dinner time, the police arrive to interview Liam. They reveal that a neighbor saw him with Olivia the night of her disappearance and promised to be in touch. Shaken, Jason hires a lawyer for his son.

The next day, the police return with a search warrant for the Casses’ home. A phone call informs Erika that Liam has been in a fistfight at school with Tyler. She goes to the school to pick Liam up and learns that Tyler attacked her son because he thinks Liam kidnapped Olivia. Madison also verbally attacks Liam, begging him to tell her where Olivia is. The principal suggests that Liam stay home from school until things cool down.

Liam’s attorney tells him he will soon be arrested based on evidence collected during the police search and the testimony of Liam’s eighth-grade English teacher, who believes Liam tried to kill him for failing him in class. When the police arrest Liam for Olivia’s kidnapping and murder, Erika publicly begs him to reveal where Olivia is, but Liam insists he is innocent. Out on bail, Liam returns home. There, Olivia’s mother surprises the Casses with a knife and threatens Liam, begging him to tell her where her daughter is. Jason eventually calms her down and calls her a taxi. As the days go by, Liam is cold to Erika because he knows she thinks he is a murderer.

Erika visits her father and is surprised by how ordinary and kind he is. He tells her that the pills he gave his lover were meant to induce pregnancy loss after she told him she was pregnant. He desperately wants to meet Liam because they look so similar. Erika leaves their meeting confused about what kind of man her father is.

One night when Jason is working late, Liam comes to Erika crying and tells her he knows where Olivia is. He takes her to an isolated cabin, where Erika sees both Hannah’s bike and Jason’s car. Jason comes out of the cabin, telling Erika that Liam has killed Hannah and Olivia. Liam tackles Jason, causing Jason to drop the knife with which he was about to stab Erika. Erika takes the knife and hands it to Liam, who stabs Jason to death. Inside the cabin, they find Hannah and Olivia hidden in a hole under the floor. Olivia has been there for the last few days, slowly starving to death. Liam helps the girls out of the hole and brings them to safety.

Erika tells the police that she killed Jason in self-defense, protecting her son from prison. A year later, Erika has become a national hero for her role in saving Olivia. Liam, still dating Olivia, returns home from a debate competition in an extremely good mood. When he goes upstairs to shower, Erika hears a news story about a missing girl from a town near the debate competition. She worries that Liam is involved in her disappearance.