All it takes is a book cover in a certain shade of yellow, or the tangy flavor of red Fruit Stripe, to transform me into a 9-year-old lying on the couch with a tower of Nancy Drew mysteries and a mouth full of gum. I can still feel that frantic need to learn who had stolen the plans, or hidden the jewels, or switched the trunks on the cruise ship. Now, though, I realize the central mystery was Nancy herself. The amateur sleuth was brave, clever and beautiful. But who was she, really? Even if you obsessed over reading every book in the series, as I did, you’d never learn much more about her. Developing the characters was never the point.

Four new middle grade mysteries take the opposite approach. Their intricate plots keep you guessing, for sure, but these stories also fulfill the promise of the best novels aimed at young readers: to shed light on the deeper mysteries of identity and self.

Take, for instance, Katryn Bury’s debut, “Drew Leclair Gets a Clue.” The seventh grader Drew Leclair may be named after Nancy Drew, but she has a skill set Nancy could only dream of. She’s grown up on true-crime stories, and her favorite book, “In the Shadow of a Killer,” is a primer on criminal profiling. When it turns out that a troll has taken over the unofficial student-run Instagram account at her school — and Drew herself is the target of the troll’s anonymous posts — she uses her profiling toolbox to figure out who’s behind the hack. Meanwhile, Drew is also dealing with a host of other worries, from her mother’s affair with her school counselor (with whom she’s left the family to go live in a yurt in Kauai) to the way her best friend, a boy, is suddenly interested in kissing.

The mystery comes to a satisfying conclusion — Drew is able to expose the culture of bullying at her school — but the story really shines when she begins to process the feelings she’s been avoiding. Does she want her mother to come back or not? Does she like boys or girls? Does she trust her friends? Drew digs deep and talks everything through.

Note the delightful relationship she has with her dad. Nancy Drew’s father, in all his wisdom, never thought to plan “Murder and Mayhem” movie nights for his titian-haired daughter.

There’s a lot going on in this book, and it can be hard to keep track of its many strands, but the cast of characters (and the community in which they live) is richly imagined.

Felix Fine, the sixth-grade protagonist of “Nothing Is Little,” by Carmella Van Vleet, is also familiar with adult crime-solving tactics. He has just joined the Forensic Science Club, where he’s acquiring the skills necessary to solve a series of “staged crimes” at his middle school. With every fingerprint he analyzes and witness he interviews, Felix hopes he will also get closer to solving another mystery: locating his birth dad.

Growth hormone deficiency has left Felix smaller than some 8-year-olds, and he’s starting daily shots to help him grow the way he’s supposed to. Felix doesn’t mind being short — he even has a collection of funny T-shirts that say things like “No, I’m not an elf.” When he discovers that his father, too, was short, it’s all the evidence he needs to launch a full investigation.

Felix’s model detective is Sherlock Holmes — he’s thrilled when another character nicknames him “Shortlock Holmes” — and the book’s title comes from a Holmes quote: “To a great mind, nothing is little.” Like Drew Leclair’s story, though, Felix’s is as internal as it is external. As he follows clues to his father’s identity, he learns about the person and friend he himself is beginning to be (while making some age-appropriate blunders).

His maturity is tested in one over-the-top scene that strains believability but also puts the rest of his worries in perspective. Felix’s problems are manageable. He may not get exactly what he wants by the end, but he gets more than he bargained for.

Chester Keene, the titular hero of Kekla Magoon’s “Chester Keene Cracks the Code,” is also a sixth grader with an absent dad. Unlike Felix, however, Chester knows the reason his father is missing: He’s a spy on a secret mission. And Chester is in training to be just like him. “Keen observation skills are a hallmark of effective spycraft,” Chester says. “You have to know everything, see everything. … Information is power. A small detail can tell an entire story.” Observing suits Chester just fine, as he prefers a life on the margins of middle school, shaped by his many rituals.

When a ferocious bully fixates on Chester, he emails his dad for help. His dad never calls or visits — he never breaks his cover — but he sends thoughtful responses full of advice. Then, out of nowhere, he sends a task, a puzzle Chester must solve with the help of a free-spirited girl named Skye. The purpose is unclear, but Chester trusts his father’s plan.

Chester is a sensitive, sympathetic character whom you root for from the first page. When Skye bursts into the school cafeteria, though, it’s as if Chester is leaving black and white for Technicolor. Together, these characters crackle — I can’t remember the last time I read such perfect dialogue.

The puzzle is clever. While it puts Chester and Skye in the way of some criminals, there’s also another scheme unfolding, and it’s a surprise. Readers might guess the secret identity of Chester’s dad, but suspense builds as we wait for it to dawn on Chester.

“Chester Keene Breaks the Code” delivers a truly fresh mystery — along with a heist, some heartbreak, some unforgettable characters and plenty of laser tag.

One of these novels is not quite like the others. “Wretched Waterpark,” the first book in the Sinister Summer series by Kiersten White, is wickedly weird. The Sinister-Winterbottom siblings have been packed off to their Aunt Saffronia for the summer, although none of them can quite remember how they got to her house. Let’s just say she’s not the warm and cozy kind of aunt. “How often would you say you need to eat?” she asks. “If I set out some food in the morning, will that be enough?” — and things only get worse from there. She leaves them at a water park and tells them a week there should be enough time to find something that has been lost. Exactly what it is or how they are supposed to find it are questions for the 12-year-old twins and their 16-year-old sister — who is always on her phone — to explore.

Fathoms of Fun has a gothic theme, with prices in Roman numerals and staff in lace collars. The water slides shoot out of gargoyles on a stone tower, and the food at the snack bar is unspeakable: jellied eel and pickled oysters, followed by a Victorian mince pie. After some adventures, however, the kids discover their mission, and the caper rolls along to its Scooby Doo-style conclusion. In their own way, the Sinister-Winterbottoms, too, are uncovering family secrets.

The mystery here is almost secondary to the humor, which is very broad — kids may crack up sooner than this reviewer did. But the darkly comic tone will appeal to anyone who loved “A Series of Unfortunate Events.”

I must admit I had a visceral reaction to White’s descriptions of Fathoms of Fun. They made me long for dazzling blue water, scorching pavement, stacks of striped towels and the scent of fried dough. If that’s not a recommendation for a summer read, I don’t know what is.

Kate Egan’s first middle grade novel, “Golden Ticket,” was published in June.

DREW LECLAIR GETS A CLUE, by Katryn Bury | 288 pp. | Clarion | $16.99 | Ages 8 to 12
NOTHING IS LITTLE, by Carmella Van Vleet | 224 pp. | Holiday House | $18.99 | Ages 8 to 12
CHESTER KEENE CRACKS THE CODE, by Kekla Magoon | 304 pp. | Wendy Lamb | $16.99 | Ages 8 to 12
WRETCHED WATERPARK (Sinister Summer, Book 1), by Kiersten White | 256 pp. | Delacorte | $16.99 | Ages 8 to 12