Percy's journey is not merely a quest to find a thief, but a profound exploration of his own identity. He grapples with the revelation of his demigod status, the mystery of his divine parentage, and the struggle to understand his place in a world where ancient myths are suddenly real. This theme highlights his transformation from an insecure, troubled boy into a burgeoning hero who embraces his unique heritage.

The narrative deeply explores various forms of family. Percy's complex relationship with his mortal mother and absent godly father forms a central emotional arc. Beyond his biological family, the book emphasizes the sense of belonging and camaraderie he finds with his fellow demigods at Camp Half-Blood and, most importantly, with his quest companions, Grover and Annabeth, who become a surrogate family unit.

At the heart of the plot is a grave injustice – Percy is falsely accused of stealing Zeus's master bolt, an act that threatens to plunge the world into war. His quest is driven by the need to prove his innocence and uncover the true culprit. This journey forces him to confront the harsh realities of betrayal, not only from mythological figures but also from those he might have considered allies, challenging his perceptions of trust and loyalty.