- "Out of the untamed frontier, danger always runs wild!"
- — Tagline, from the front cover
Survival of the Fittest is the 120th book in the The Hardy Boys Casefiles series.
Frank and Joe have come to the ruggedly beautiful mountains of Utah to test their wilderness skills. But on their very first day out, after a frayed rope nearly sends Joe plummeting to the bottom of a rocky ravine, they discover that the challenge will be far more perilous than they imagined. This will be a test of survival!
The Hardys have stumbled upon a deadly scheme of greed and sabotage. But to uncover the secret behind it, they'll have to follow the trail of infamous outlaws -- Butch Cassidy and his Hole in the Wall gang. The gang may be long gone, but a new breed of desperado is on the loose...and they're gunning for Frank and Joe!