An urgent call for help from their father's friend, chemist Sam Gentle has drawn Frank and Joe across country to northern Arizona. The cryptic message offers no clue to the danger he's in, and it's one secret he will never reveal. Soon after their arrival, the boys find Sam Gentle lying at the bottom of Wolf's Tooth Canyon -- a victim of murder.

The Hardys suspect that Sam's research at Titan Chemical Industries led to a discovery that turned him into a target for terror. But his death was only the beginning. The chemist left behind a deadly hidden legacy, and Frank and Joe are all that stands between the killer and Sam's daughter Tiffany!