The Mystery in the Old Mine

After Garth Trimmer discovers that his apartment has been ransacked and nothing of value stolen, he calls on the Hardys to discover who was responsible. While looking over the mess a letter arrives by courier telling Garth that his sister has been kidnapped and that if he wants to see her again he is to bring “the notebook” to the covered bridge in Ridge City, Pennsylvania by midnight that night. What notebook was the letter writer referring to and what is going on in Ridge City, an abandoned mining town with underground fires running rampant? It is up to Frank and Joe Hardy to figure out.