The Hardy Boys 45: The Mystery Of The Spiral Bridge by Franklin W. Dixon.

"The Hardy Boys 45: The Mystery Of The Spiral Bridge"
Armada Books
Published in 1974, first Armada publishing.
First published in 1972 by Grosset & Dunlap.
Contains the Hardy Boys story The Mystery Of The Spiral Bridge by Franklin W. Dixon in 156 pages, with black and white illustrations.
"The Hardy Boys track down the saboteurs who kidnapped their father, and have to keep them from blowing up a bridge near Boontown, Kentucky. The bridge is being built by Tony Pritos fathers construction company. Mr Hardy is ill most of the story. The Villains are mostly ex-crooks who wants that area of the bridge for themselves."