No friendships worthy of Flaubert’s exacting pen emerge from the Ursuline convent of Emma Bovary’s schooldays. Blame it on the local black market. Out of sight of the nuns, a matronly seamstress stashes books “full of love and lovers” in her apron smocks and slips copies to the older girls — hypnotizing tales of moonlit crossings, fainting damsels, horses ridden to death by perpetually late beaux. Only lovers (noblemen in...