This is book number 40 in the The Boxcar Children Mysteries series.
The Boxcar Children are going on a canoe trip with Grandfather and Aunt Jane. They enjoy paddling across the sparkling lake and camping under the stars. But their trip really gets interesting when they find a mysterious riddle leading them to hidden treasure!
The Boxcar Children Series was created by Gertrude Chandler Warner, a teacher, when she realized that there were few, if any, books for children that were both easy and fun to read. She drew on her own experiences in writing the mysteries. As a child, she had spent hours watching trains near her home, and often dreamed about what it would be like to live in a caboose or freight car. In each story, she chose a special setting and introduced unpredictable, unusual or eccentric characters, to help highlight the Aldens’ independence and resourcefulness. Miss Warner lived in Putnam, Massachusetts until her death in 1979.