Mountain-Peak Mystery — Carolyn Keene

Tammi Hodge, a fourteen year old orphan, is searching for the secret disclosed in a manuscript written by her grandfather. But the manuscript has been stolen, and a copy of it seems to have disappeared. Tammi asks the Danas to help her find the hidden duplicate.

Louise and Jean take the case, but soon realize they are in a dangerous race with unknown enemies who are also hunting for the duplicate manuscript. The Danas encounter new threats to their lives at every turn as the thieves try to scare them off the Hodge property. Tammi is almost kidnapped, and a strange earthquake rocks the mountaintop home.

The Danas' discovery of a hidden tunnel containing a strange gray powder is followed by an even more exciting find. But their jubilation ends when they realize they are trapped in the tunnel. Readers will thrill at the Danas' rescue, their defeat of cunning adversaries, and a fantastic revelation that goes back to prehistoric times.