Kidnapped at Birth?

by Blue Balliett

Like Marvin's detective work unraveling his true identity, this book puts you in the shoes of two kids piecing together an art heist through careful observation and hidden clues. Balliett has that same playful confidence in her young protagonists' ability to solve genuine mysteries, and the illustrations scattered throughout create that same sense of discovering secrets on the page itself.

by Trenton Lee Stewart

This one captures that same delight in a child realizing they're actually *special*—but instead of discovering royal blood, your protagonist finds out he's part of an elite group of gifted misfits on a secret mission. Stewart builds the same kind of escalating absurdity mixed with genuine stakes that Sachar does, where the ridiculous premise (a secret society recruiting through a puzzle test) somehow becomes completely believable.

by Barbara Taylor

Here's your surprise pick: this is historical fiction, not fantasy, but it has that same DNA of young people discovering hidden truths about themselves and their world. Two girls in Victorian London realize they're living the lives of famous philosophers' daughters—and they use that knowledge to solve real crimes. It's got Sachar's humor about identity and belonging, but grounded in actual history in a way that might expand what you think middle-grade adventure can do.

by Mari Lu Robbins

Published in 1967, this is a masterclass in the same thing Sachar's doing—a child running away from their ordinary life only to discover something profound about who they actually are. Konigsburg's New York City and her mysterious millionaire are rendered with the same kind of specificity and warmth, and like Marvin, your protagonist learns that the real mystery was never about the external secret, but about self-acceptance.

by Enez Whipple

Two best friends discover they're not who they thought they were—one's a noble, one's a peasant, and their entire friendship is built on a lie. But instead of falling apart, they lean into the adventure of figuring out what's real about themselves beyond their origins. It has that same tone where the outlandish premise (a guild that trains adventurers) serves as a framework for genuinely exploring what it means to belong somewhere.