The Hundred Year Mystery — Carolyn Keene

A treasure in jewels and gold coins is hidden somewhere on the Beacon College campus! But where is it? And where is the codicil in which John Beacon, founder of the school, revealed its location?

These are the questions the Danas are asked to resolve by their uncle, Phil Kenmore, president of Beacon, as the college approaches its centennial, the date on which it is to receive the fortune. During their investigation, Louise and Jean explore spooky caves and are almost drowned at the site of a Viking mishap from many centuries ago.

But even before their hunt begins, the Danas are harassed by extortionists who claim to have the missing codicil. The girls' efforts are sabotaged over and over again by these unscrupulous enemies who will use any means -- even the bombing of the school -- to terrorize the Danas and hamper their search. Their resolve unshaken, the Danas follow every lead until, through a study of ancient Viking symbols and customs, they outwit their enemies in a breath-taking finale.