The Secret Of Lost Lake, The Dana Girls Mystery Stories, number 24 in the series. Author: Carolyn Keene (who also wrote the Nancy Drew books). Hardcover, 174 pages. Publisher: Grosset & Dunlap, no 9224, published in 1963. 

While staying at Lost Lake, the Dana girls become embroiled in a mystery involving a missing treasure. The treasure, rumored to be hidden in or near the lake, attracts the attention of various suspicious characters. The sisters must use their wit and resourcefulness to piece together clues, avoid dangerous situations, and uncover the truth about the treasure's location. 

The book covers, spine, binding, and inner pages are all in very good plus condition. There is a name written very faintly in pencil at the top of one page.