In the 1950s, Laura Butler and her seven-year-old son, Cody Butler, embark on a journey to a secluded home in California, seeking refuge from her abusive ex-husband. However, their new life is overshadowed not only by the looming threat of his return but also by a mysterious monster that lurks in a nearby lake.
As they try to settle into their new environment, Laura juggles sending Cody to school, preparing his lunches, and working at a typing job. Meanwhile, Cody becomes increasingly frightened by an entity that seems to haunt him at night. After a direct encounter with this ominous creature, he begins to refer to it as the "pretty lady from the lake." Despite this strange familiarity, Cody longs to return home and often argues with his mother about it. He displays signs of sadness and depression, especially as his birthday approaches.
In a bid to cheer him up, Laura organizes a birthday party, sending out invitations to his classmates. However, Cody insists that no one will come, even as she encourages him to give it a shot. They go all out to decorate their home with colorful balloons and prepare delicious meals, but the day ends in disappointment when not a single guest arrives. Overwhelmed with despair, Laura turns to alcohol and ultimately quits her job.
In a frantic attempt to find Cody, she heads to his school only to discover he is missing. Seeking help, she approaches a policeman for assistance. This leads her to the police station, where a woman prompts her to recall an incident from the previous year when Cody had an accident. Reliving the moment, Laura recounts shopping for groceries while her husband watched their son. Tragically, Cody fell into the pool, and by the time she returned, it was too late. She believes the paramedics revived him, but a sense of dread hangs in the air. After requesting water, she exits the police station feeling distraught.
Upon returning home, Laura is met with the heart-wrenching sight of Cody waiting for her. He pleads with her to let him go, insisting he belongs with the "pretty lady of the lake." The shocking reality dawns on her: Cody had died in the accident, and her mind had conjured this 1950s existence as a way to cope with her unbearable grief. The truth is that the current year is actually 2022, and everything she believed was a mere illusion.
Finally, after a tumultuous internal struggle, Laura makes the heart-wrenching decision to allow Cody to accompany the "pretty lady in the lake." In doing so, she achieves a profound sense of peace, releasing herself from the shackles of her delusion. Laura leaves behind her California home, marking a significant step toward healing and acceptance.
