Mary and Mildred need a place to share Their Secret. At first the bough of the apple tree serves the purpose, but then father hits on a more elegant idea -- a treehouse. And so with great fanfare the new domain comes into being. Even little sister gets into the act -- as a sentry on a soapbox of her own. To celebrate the occasion, the girls hold a tree housewarming at which a nominal admission is charged for cookies and entertainment, both homemade. Suspense builds -- for although readers will delight in the girls' exciting summer in and around the treehouse, they are never let in on the secret. Of course a surprise ending is in store. The secret? -- that there is no secret, just Mary and Mildred pretending. A favorite established author captivates a feminine entourage this time in an entertaining book for treehouse reading.