Many teen-agers will go to great lengths to keep their diaries private—I kept a little key for mine in a wooden jewelry box, which I guarded jealously—but the children’s book author Beatrix Potter took it to an extreme. Between the ages of fourteen and thirty, she fastidiously recorded observations about her stiff Victorian world in several journals. Her parents, descendants of wealthy cotton merchants in the North of England, were rich and exceedingly proper. Perhaps to protect her work, Potter wrote in a minuscule handwriting using a code that only she could understand. Her journals remained a mystery until 1958, when a collector, searching through them, identified a passing reference to Louis XVI, and then painstakingly decoded years’ worth of Potter’s innermost thoughts. (Fans are nosy, too).