An anonymous diary is a mystery with handwriting that is difficult to decipher. It is filled with technical drawings and chemical formulas. Was the destructive explosion an accident or an act of revenge?

A carrier pigeon furnishes Nancy with a clue to a mysterious retreat.

A rare Chinese vase is stolen from a pottery shop. Nancy and the owner of the shop feel that locating "the leaning chimney" will provide the clue to the vase and other stolen articles.

An unusual hex sign leads Nancy Drew to Pennsylvania Dutch country in pursuit of a thief who stops at nothing to get rid of her.