Hardy Boys mystery stories

After a dying criminal confesses that his loot has been stashed "in the tower," the Hardy boys make an astonishing discovery.

Determined to learn the secret of the old mill, Frank and Joe employ a clever ruse to gain entrance and become trapped. There they unravel two mysteries, one involving a counterfeiting case and the other a national security case their father is working on.

The Hardy boys' search for stolen gold leads them to an abandoned mine where, in the depths of the earth, they are attacked by outlaws.

When the Hardy boys reached the caves, they came unexpectedly upon a queer old hermit.