Sylvia Plath began keeping a diary as a young child. By the time she was at Smith College, when this book begins, she had settled into a nearly daily routine with her journal, which was also a sourcebook for her writing. Plath once called her journal her "Sargasso," her repository of imagination, "a litany of dreams, directives, and imperatives," and in fact these pages contain the germs of most of her work. Plath's ambitions as a writer were urgent...