Turtles All the Way Down by John Green is about two teenage girls who try to find a missing billionaire. Aza Holmes, the main character, has Obsessive Compulsive Disorder (OCD), which, for her, is characterized by an obsession with germs and illness.

When she is with her friends and trying to focus on other things, Aza thinks,

I couldn’t stop wondering whether there was something wrong with the microbial balance of power inside me.

Her OCD is so severe that she often reopens a cut on her finger to release blood and let out any bacteria that she thinks might be inside her. Aza’s stomach has also been hurting. She recalls that

excessive abdominal noise is an uncommon, but not unprecedented, presenting symptom of infection with the bacteria Clostridium difficile, which can be fatal.

Not for the first time, she opens the Wikipedia page for the bacteria and reads it.

During their hunt for the missing billionaire, Aza falls for the billionaire’s son Davis. He also falls for her, and they begin dating. One night he texts her saying,

I like us. For real.

He also gives Aza and Daisy the reward that they would have earned if they had found his father, because he does not want them to look for him. Aza tells Daisy that

Davis said it was worth it to him, that he’d rather give us the reward than have us snooping around.

Daisy is Aza’s best friend, and she writes Star Wars fan fiction. When Aza reads it, she believes some of it is based on her, and she thinks it paints her in an unflattering light. During the ensuing fights, Daisy tells Aza something her boyfriend, Mychal, said. She says,

Mychal said once that you’re like mustard. Great in small quantities, but then a lot of you is . . . a lot.

The fight that results from that leads to Aza wrecking the car her father left her, being hospitalized with a lacerated liver, and drinking hand sanitizer due to her fear of the bacteria in the hospital.

Even after Daisy and Aza find the body of the billionaire, there is no happy resolution. Green writes:

You’d think solving mysteries would bring you closure, that closing the loop would comfort and quiet your mind. But it never does. The truth always disappoints. As we circulated around the gallery, looking for Mychal, I didn’t feel like I’d found the solid nesting doll or anything. Nothing had been fixed, not really. It was like the zoologist said about science: You never really find answers, just new and deeper questions.

Aza tells her mother that she is not going to tell anyone except Davis: if the body is found, the money will go to the billionaire’s pet lizard rather than to his sons. Aza’s mother responds by saying the following:

“The madness of wealth,” my mother mumbled. “Sometimes you think you’re spending money, but all along the money’s spending you.” She glanced down at her cup of tea, and then back up to me. “But only if you worship it. You serve whatever you worship.”

Aza responds, telling her that they need to be careful what they worship. As she leaves the room, she wonders what she will worship in the future.

Davis decides to tell the police where to find his father. He believes it is the right thing to do for his younger brother. However, it means they have to move and start a new life elsewhere. After he leaves, Aza reflects on her feelings for Davis:

I thought, lying there, that I might love him for the rest of my life. We did love each other—maybe we never said it, and maybe love was never something we were in, but it was something I felt.