super fun! less a "mystery" book than a series of loosely organized vignettes with small but bizarre (/ridiculous) puzzles at their core, solved by a rich, young お嬢さん and her enigmatic chauffeur ベッキーさん. the protagonist is someone i thought i'd dislike on paper (...no pun intended) but quite liked in the end - there's something almost touching about the precocity of her observations, which are tempered by self-awareness and compassion.
the fun of the book is mostly due to the setting (early showa) - the protagonist reads ranpo and tanizaki, does ginbura, hangs out with the aristocracy, watches charlie chaplin films (there's mention of his visit to japan, too, though puzzlingly no mention of the 5/15 jiken), etc. the references are perhaps rather artificial/shoehorned in but i admit i still enjoyed it all.