THIS COLLECTION OPENS in 1941, when Patricia Highsmith introduces the first of her diaries—Diary 1a—to be kept in tandem with her notebooks. On April 14, 1941, she writes, “Je suis fait[e] de deux appétits: l’amour et la pensée [My appetite is twofold: I hunger for love and for thought].” How much experience is needed, she wonders, in order to write about it? To what extent does one side of this equation feed off the other? [...]