Kit Lowell is a teenager reeling from the death of her father in a car accident the month before. Unable to face the thought of talking normally to her friends at lunch, she sits with David Drucker, a classmate with borderline Asperger's, whose bluntness she finds refreshing. The two form an unlikely friendship and budding romance. Kit asks David to investigate the physics involving her father's accident to see if there was any possible way it could have been avoided.
What to Say Next contains examples of:
- Big Sister Instinct: David's sister Lauren, aka Miney, used to be the most popular girl at Mapleview High before she went to college last year. Nobody dared to bully David because she'd make them pay.
- Blonde, Brunette, Redhead: Jessica, Willow, and Abby, referred to as "The Popular Bitches" in David's notebook. As far as Kit can tell, their friendship is built mostly on hair color optics.
- Dedication: "For Josh, the president of my first tribe. So happy you let me keep my lifetime membership. And for Indy, Elili, and Luca: my heart, my reason, my home, my tribe, my life."
- Due to the Dead: Kit wears one of her father's work shirts to school as a tribute to him.
- First Kiss: David kisses a slightly drunk Kit at a party. She assumes he's done it before, but he's actually watched YouTube videos about kissing technique.
- Heartbreak and Ice Cream: Kit and her mother both deal with her father's death by eating, especially ice cream and bacon.
- He Cleans Up Nicely: To help David get Kit to date him, Miney takes David to the mall for a new haircut and some cooler clothes. David doesn't like the way the clothes feel, but everyone in school is amazed by the transformation. Kit's friend Annie asks, "Is that why you've been sitting with him? You knew there was, like, this freakin' hot guy under all that hair?
- If You Ever Do Anything to Hurt Her...: Miney warns Kit, "You're probably good people too, but just so you know, I love David more than life itself, so if you hurt my brother in any way, or if you even think about hurting him, I will ruin you. I may not still live here, but I can still do that."
- I Just Want to Be Normal: David very much wishes he could upgrade himself to be more normal, so he'd know what to say in social situations.
- I Need to Go Iron My Dog: Uncle Jack, who is not actually Kit's uncle but her father's best friend, drops by her house to talk to her mom about the will, but her mom says, "Wow, it's getting late and I actually have a lot of work to do," and flees the room. She's avoiding him because she was having an affair with him. Kit's parents were on the verge of divorce at the time of the accident.
- Maligned Mixed Marriage: Kit's mother is a second-generation Indian immigrant whose parents tried to assimilate her into American culture as much as possible when she was a kid, and then were surprised when she married a white guy. Kit's grandparents accepted her, but always disapproved of her father. After her father's death, her mother didn't even tell her parents until after the funeral, which Kit thinks is because she knew they wouldn't come.
- Mouthful of Pi: David repeats hundreds of digits of pi to himself when he's stressed out.
- Playing Sick: When Kit leaves class to investigate the accident, she tells Mr. Schmidt, "I'm going to the nurse." David follows her a few minutes later by saying, "I need to empty my bowels."
- Portmanteau Couple Name: In-universe example. When Justin and Jessica were going out, everyone called them "Justica." Every time Kit heard it, she thought, I can't wait to go to college.
- Sensory Overload: David wears big noise-cancelling headphones in the hallways and during lunch to deal with this.
- Signature Scent: Kit notes that David has a sweet lemony smell.
- Sleepy Depressive: David spends three days doing almost nothing but sleeping after his Secret Diary is leaked online under the name "The Retard's Guide to Mapleview."
- Swirlie: When David was in middle school, Justin Cho lured him into a bathroom stall, saying he had something he wanted to show him. Instead he gave him a swirlie and then stuffed him in a locker. People called him "shithead" for months afterward, and the incident prompted Miney to make a Do Not Trust list of people David must not engage with under any circumstances.
- That's What She Said: While trying to give David relationship advice, Miney says, "I'm not letting you blow this." David replies "That's what she said," a joke he learned a few weeks ago and has been waiting for an opportunity to use ever since.
- Troubled Fetal Position: Kit walks out in the middle of math class. David follows her and finds her on the floor of the concessions hut with her knees pulled to her chest.
- You Should Have Died Instead: Kit tells her mom, "I wish it was you who died. Not Dad. You. It's not fair," because she's mad at her for sleeping with Uncle Jack.
