Frank and Joe Hardy, while delivering important papers to a lawyer in Willowville for their father, ar almost driven off the road by a reckless driver. Then they learn that their friend Chet’s yellow jalopy has been stolen, possibly by the same red-haired driver! Things take a startling turn when a dying criminal confesses that the loot he stole is stashed "in the tower"—leading the Hardy Boys to make a startling discovery.—Goodreads.com.
This is the revised 1959 version of the story (updating the 1927 original of the same title).