The House Across the Lake is a thriller novel by American author Todd Ritter, writing under the pen name Riley Sager, published through Dutton in 2022. The novel is a fast-paced mystery wherein a woman uncovers secrets about her lake house neighbors and herself as she plays voyeur through a pair of binoculars. Filled with unexpected twists and turns, The House Across the Lake has been compared to Alfred Hitchcock’s Rear Window and praised for its modern take on the genre. In March 2023, it was reported that Netflix will adapt the novel into a feature film.

Content Warning: The source material includes depictions of violence, murder, suicide, and substance misuse.

Plot Summary

Casey Fletcher is a 35-year-old widow who returns to her family’s lake house in Vermont after a downward spiral following her husband’s death. Leaving behind her career and public life, she settles in on the shores of the dark, unfathomable Lake Greene and prepares to spend her days drinking and trying to avoid memories of the past.

One morning, she rescues her neighbor from drowning and sparks up a friendship that will have a lasting impact on her summer. Her neighbor is the beautiful Katherine Royce, a former supermodel married to the CEO of a tech company called Mixer. The evening after she rescues Katherine, the Royces show up at her dock with an expensive bottle of wine. But when Katherine passes out in the yard, the evening is cut short, and Casey is left with some concerns.

The next day, Casey begins spying on the Royces with a pair of binoculars. Her voyeurism is made easy by the Royces’ glass wall that faces her house and allows her access to their lives. While watching, she begins to see disputes between Tom and Katherine that make her wonder about their marriage. Then one night she witnesses a domestic dispute in which Katherine hits Tom and then stares directly at Casey through the glass wall.

Although she is severely hung over and disoriented, the next morning Casey thinks she hears a scream from across the lake. Feeling worried about her newfound friend, she drives over to the Royces’ to discover Katherine is gone. Tom tells her that Katherine returned home to New York; but when Casey investigates with the help of her cousin, she discovers that Katherine hasn’t been by their building. After seeing a fake Instagram post from Katherine, Casey decides to visit another neighbor at the lake, Boone Conrad, to ask if he heard anything. Boone confirms that he also heard a scream that morning. The two of them watch the Royces’ house and witness Tom acting suspicious, So, they contact Boone’s friend, Detective Wilma Anson.

The next day, Casey decides to break into the Royces’ house. She narrowly avoids being caught by Tom, and in the process discovers Katherine’s cell phone has been stashed in a drawer and someone has web searched a man who poisoned his wife. After returning home, she calls Wilma Anson back to her house so she can analyze the broken wine glass that Katherine dropped in her yard for traces of poison. While there, Wilma tells Boone and Casey some confidential information: she is currently working on the case of a suspected serial killer of three young women: Megan Keene, Toni Burnett, and Sue Ellen Stryker. One of the suspects is Tom Royce.

Casey and Boone begin to watch the Royce house together, and in doing so grow closer. Boone suggests that they go into town to see what they can find out, and while in town they have a frank conversation about alcohol. Boone tells Casey that sobriety is possible and shares his own traumatic story; after his wife’s death, he showed up to a call while drunk and nearly shot a man, resulting in a six-month suspension. Although Casey is drawn to Boone, she still feels compelled to go home alone and binge drink to avoid the memories at the edges of her mind.

That night while drunk and spying on the Royces’ house, Casey sees Tom watching her with his own pair of binoculars. He then gets in his car and drives to her house while she scrambles to lock the doors and turn off the lights. Beating on the door, he tells her he knows that she has spied on him and broken into his home. Tom claims she doesn’t understand the situation and should leave him and Katherine alone.

However, Casey also begins to suspect Boone when she discovers he has been lying to her about his relationship with Katherine. Far from being mere acquaintances, the two had a brief summer flirtation that culminated in a kiss. Casey wonders if Boone has motivations as a jilted lover and considers the possibility that he had been poisoning Katherine rather than Tom. She calls Wilma Anson with this new information, but Wilma is loyal to Boone, and Casey feels alone.

As a storm comes in, Casey sees Tom go to an abandoned house in the neighborhood and follows him. There, she finds Katherine tied up in the basement and believes Tom is holding her captive. But Tom tells Casey that Katherine is not herself, that she has been possessed by the spirit of someone else. When Casey talks to Katherine, she realizes that she is talking to Len. It’s his mannerisms, his speech patterns, and his memories that come out of Katherine, including one that only he and Casey know: that Casey murdered him.

All the memories that Casey has been struggling to repress come rushing back in. Casey recalls the morning she found evidence of the murders of the three missing girls in Len’s tacklebox and, after drugging him, killed him by pushing him into the lake. Casey is terrified and determined to end Len’s reign of horror, believing Katherine has truly been possessed.

Casey brings Katherine/Len to her home, tying Katherine to her childhood bed and beginning her private interrogation. Amid the raging storm, Casey asks Katherine/Len about Len’s murders, determined to find out where he has buried his victims. She makes a deal with Katherine/Len that if she shows her, Casey will release Katherine/Len, though secretly intends to sacrifice herself to save Katherine. Katherine/Len shows her where the girls are buried in the middle of Lake Greene, and then she kisses him, pulling his soul from Katherine and into her body. Once the transfer is complete, she jumps in the lake with an anchor tied to her. But Katherine saves her, and the two think their troubles have ended.

After killing Len a second time, Casey confesses her husband’s crimes to Wilma Anson and directs her to where the bodies of the victims are buried. Feeling liberated from her past, Casey celebrates by pouring her liquor down the drain. However, Casey realizes that certain questions are still unanswered—such as why Katherine almost drowned even before Len possessed her. Casey realizes with horror that Tom is still suspect, and at that very moment he sneaks up and tries to kill her. The two grapple and Tom dies in the lake water but is repossessed by Len, leading his body to become reanimated. However, Casey smashes the last remaining bottle of wine and kills Len within Tom’s body a third and final time.

In the final section, several months have transpired and Casey has decided to go sober, surrounded by her family and new friends. As she slowly rebuilds her life, she feels more confident in herself and her ability to handle whatever comes next.