At the beginning of the film, we meet Peter Hadley (Jeremy Strong), who is intently listening to a woman, Bogart (Fairuza Balk), share a profoundly emotional story about her experience of undergoing her fourth abortion. She describes the lonely return home from the clinic and how her boyfriend, who was there, noticed her arrival. Attempting to hide her feelings, she pretends to be asleep but ultimately breaks down, expressing deep regret and a wish that her baby were still alive inside her. Her pain is palpable as she confides feelings of emptiness, stating that she wants to end her life and is incapable of feeling anything during intimacy.
As the camera zooms out, we discover that Peter is actually a medical student taking an exam in front of his peers and instructors. It becomes clear that Bogart's harrowing account is merely a theatrical performance as part of his evaluation, and her role as a depressed woman is scripted. When it's Peter's turn to comment on her condition and give recommendations, he becomes engrossed in her narrative, battling his own rising despair. In an attempt to contribute, he finally suggests that Paxil might be an appropriate prescription. However, his mentor sarcastically questions this choice, leaving Peter feeling anxious and uncertain as he remains silent.
In an awkward transition, we see the film's title, "Humboldt County," as Peter walks through the corridors of the medical school, his demeanor heavy with nerves and disillusionment. Later, he encounters the actress outside his teacher's office, who offers him a piece of yellow paper and emphasizes a performance happening that night. Upon entering his mentor's office, he learns that he has been denied acceptance into a prestigious residency program. Peter is taken aback, pleading his case by explaining his exhausting preparations, but his father, the head teacher, declares his disappointment, suggesting that Peter's performance put lives at risk.
A frustrated Peter finds himself in the bathroom, crumpling his rejection letter before anxiously trying to ingest it in his upset state. Edging towards embarrassment when another man appears, he eventually spits out the letter, muttering "idiot" to himself. The somber Peter then waits at a bus stop, introspective and downcast. Glancing at the yellow paper, he sees it advertises Bogart's jazz performance that night.
The narrative shifts to a lively bar where Bogart captures the crowd's attention with her captivating jazz singing. Peter walks in, filled with a mixture of hope and trepidation as their eyes meet. After her performance, they share an intimate yet awkward conversation that leads them back to her motel room. As Bogart begins to undress him, Peter nervously asks if she is an actress or a singer, to which she responds playfully, revealing that these are merely side gigs for her. In a moment of vulnerability, he mistakenly assumes she is a prostitute, making for a humorous yet embarrassing exchange. She laughs it off but like a breath of fresh air, she breaks down barriers, reminding him that "a girl can just have casual sex" without judgment.
Their chemistry ignites, leading to an evening of passion. Afterward, in a peaceful moment, Peter asks where Bogart is heading as she starts to dress. She invites him to join her, and soon we find them on a long drive, with Peter appearing extremely fatigued. Bogart's vibrant storytelling reveals that they are headed to her home along the picturesque Humboldt County coast. The scenic drive showcases stunning mountainous landscapes, a stark contrast to Peter's earlier life struggles. Eventually, he awakens alone to find Bogart standing on a cliff overlooking a breathtaking sunset, affirming she has indeed brought him home.
