Mystery of the Aztec Warrior, The (Hardy Boys #43) by Franklin W. Dixon

The handwritten will of a deceased world-traveler is strange and mysterious. Its cryptic instructions are to deliver “the valuable Aztec warrior to the rightful owner, a descendant of an Aztec warrior.” Frank and Joe Hardy have only one slim clue to work the name of a complete stranger who can help. Despite the harassments, the threats, and the attacks made upon them, Frank and Joe unravel clue after clue in their adventure-packed search for the living descendant of the mighty Aztec nation which once ruled in Mexico.

It takes as much high courage as clever deduction for the young detectives to defeat their ruthless foes and to decipher the fascinating secrets of the strange and mysterious will.