Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Sarcastic, Spunky, and Skeptical
Sarcastic and Spunky
When Nora describes her new bio partner, Patch, to Dorothea, she says, "He's tall, dark, and annoying" (2.10), a sarcastic variation on the expression, "tall, dark, and handsome." Nora's voice is full of this kind of spunk and sarcasm throughout the book, and as our narrator, she sets the tone.
Nora isn't quite as adept at wisecracking as her best friend, Vee, but even as the events in the book become increasingly dire, Nora manages to keep her sassy pants on, and Patch does a fair job of firing back. For example, after Nora is savagely attacked by Dabria in her house, she goes looking for Vee at the movie theater. At this point, she's still leery that Patch is out to kill her, so when he corners her in the girls' bathroom, she tells him to back off:
"You're impinging on my private space," I said, inching backward.
Patch gave a barely-there smile. "Impinging? This isn't the SAT, Nora." (26.67-68)
The text loves to pack in these kinds of sarcastic zingers.
Skeptical
There is also a lot of mystery in the book. Who is Patch? Who is the person in the ski mask? Why can Nora hear other people's thoughts in her head, and why does it seem like her memory is being altered? Nora isn't readily cued into all the strange happenings; instead she asks questions and double guesses things. In fact, one of her go-to lines is "what's going on?" More than once we see Nora sleuthing around for information—even donning ridiculous disguises and flitting off to Portland on her own to do so—and many of her exchanges with Patch go something like this:
"Well?" I demanded […]. "Do you have anything to say?"
"No."
"You have no idea what happened to Vee?"
"Again, no." (16.81)
Given the fact that Nora is trying to get to the bottom of the violent attack against her friend, we'd say frustrating moments like these definitely keep the mystery alive as the book unfolds. Nora doesn't believe Patch—that's why she puts him on the spot twice in a row—and we find her in similar scenarios, skeptical of what she's being told, time and again.