The Long Secret is a children's novel written and illustrated by Louise Fitzhugh that was released by Harper & Row on October 27, 1965.

Her summertime friend, twelve-year-old Beth Ellen Hanson, sometimes called Mouse, is also in Water Mill with her paternal grandmother.

Mysterious anonymous notes start showing up all over town; they have a religious slant and expose the "sins" of the recipients.

Harriet drags Beth Ellen along on spying expeditions directed against Bunny, the piano-playing manager of the local hotel, and the Jenkinses, an eccentric southern family preoccupied with moneymaking schemes.

Beth Ellen learns that her entitled rich mother, Zeeney, who left when she was five, is returning from Europe with her new husband, Wallace.