In the fifth ''Princess Diaries'' book, Mia, a hilarious New Yorker who happens to be the princess of fictional Genovia, struggles with a citywide restaurant strike, turning 15, and trying to wrangle an invite to the prom. Laced with a smart-alecky feminism, the book, like, totally gets the tone of precocious private-school nerds. Cabot pumps up the madcap plot with amusing pop-culture and highbrow references: Mia's imperious, chain-smoking Grandmère has named her dog Rommel, a sly suggestion of how the dowager princess ''has embraced the dark side...fully.... But I guess even Darth Vader had his moments.'' Picture Mia as a funnier (and more articulate) sister to Nancy Drew or the Baby-Sitters Club.