Princess Principal unfolds in an alternate 19th-century London, where the discovery of Cavorite has accelerated military technology and pushed the Kingdom and the Commonwealth of Albion into a quiet, relentless conflict. A massive wall cuts the city in two, and espionage becomes the decisive weapon in a war fought through false identities, secret meetings, carefully staged betrayals, and information traded in the shadows. Behind the refined atmosphere of Queen's Mayfaire school, five girls pose as students while working as undercover agents for the Commonwealth, moving through the city with the constant risk that one mistake could expose everything.
Dorothy, an experienced driver with a striking personality, leads a team whose members each bring a specialized skill to the field: Ange le Carré, a cold-blooded liar and expert sharpshooter; Chise Toudou, a proficient samurai; and Beatrice, a voice-mimicking specialist. Alongside them stands Princess, whose place at the center of Albion's divided capital ties the group's covert missions to the larger struggle between the wall's two sides. Their assignments carry them through a dark world of conspiracy, mystery, infiltration, disguise, and car chases, where every operation can change the balance of power and their only clear objective is to complete the mission and disappear before the enemy notices.