Konigsburg masterfully crafts this story with a small cast of characters. In fact, only three characters take the stage for readers. Claudia and Jamie are at the forefront, while Mrs. Frankweiler, the only other significant character, serves as the narrator. Although he never makes an actual appearance, Claudia and Jamie's grandfather, Saxonberg—a lawyer—is the intended audience of Mrs. Frankweiler's tale and the target of her sharp remarks, possibly even her affections. Other characters, like Claudia's parents, siblings, and classmates, serve as mere background.

She glanced at Jamie, her eyes widening, "M for Michelangelo!"

Claudia's adventure is rooted in one of the book's central themes. As the eldest of four siblings, the eleven-year-old protagonist is starting to develop a sense of identity. However, she feels that her family fails to recognize her growing maturity. She is still tasked with the same old chores and engages in the same old debates about which TV show to watch. Her academic success, in her view, goes largely unnoticed.

By running away to the museum and withholding her help from her parents, Claudia seeks to demonstrate her worth. In her absence, she believes they will realize how much she meant to them, how they mistreated her, and how much she has matured. While she is correct in recognizing her own growth, Claudia has not yet learned everything she needs to know. Her museum journey ultimately teaches her that what truly matters is not others' opinions of her but her own self-awareness. Jamie and Angel are the key figures who help her come to this understanding.

Claudia makes a sensible choice by selecting Jamie as her partner because he has more than twenty dollars—money he mostly acquired by cheating at the card game, War. Jamie will handle the finances, while Claudia will be the strategist, planning their escape and ensuring they can live in the Metropolitan Museum. As the story unfolds, Claudia discovers that Jamie's worth extends beyond his money. Together, they manage everyday tasks like eating, sleeping, and doing laundry, which become adventures in the museum setting. Their mutual reliance teaches Claudia that family is more than just TV disputes and babysitting grievances. She learns that cooperation can be enjoyable and that depending on and being depended upon is a vital part of life.

Indeed, this collaboration develops into trust, enabling them to succeed in their mission to uncover Angel's true origins. The museum purchased Angel at an auction for just $225, but if the statue is confirmed as Michelangelo's work, its value could exceed $2,250,000. While the potential financial gain captivates Jamie, Claudia is more intrigued by the mystery. Together, they investigate the statue's history but make no progress until Claudia decides to approach Mrs. Basil E. Frankweiler, the original seller of the statue collection. For Claudia, discovering the statue's history becomes paramount, as she starts to identify with Angel. Both the statue and Claudia harbor a secret that no one else knows, influencing their perceived value and worth.

During Claudia's conversation with Mrs. Frankweiler, she realizes a truth she has always known: that worth is intrinsic, not dependent on external validation. She and Angel possess inherent value regardless of others' recognition. Mrs. Frankweiler understands this, as she had documents proving the statue to be Michelangelo's "lost Cupid" when she sold it. She believes the secret holds more value than the fame that comes with public acknowledgment and imparts this wisdom to Claudia and Jamie. They become custodians of the secret, but only if they preserve it long enough to inherit the documentary evidence from Mrs. Frankweiler.

Ultimately, Claudia returns home, confident in her self-worth and prepared to engage with life on a more mature level. More importantly, she has discovered the true secret within herself, a revelation that has justified all their efforts.