The Mystery of the Moaning Cave
El Diablo -- The Devil! The very name of the legendary outlaw strikes fear in the hearts of California ranch owner.

Many years ago, the young El Diablo disappeared into a mountain cave, never to be seen again. But the ranchers think he may still be alive -- especially now that an eerie moaning sound is coming from his old hideout.

The Three Investigators set out in the dark of night to explore the moaning cave -- and they soon wish that they were armed with more than a flashlight!
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EDITIONS
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    •  
    • Jul-1968
    • Random House
    • Paperback
    • ISBN: 0394814231
    • ISBN13: 9780394814230
    •  
    • May-1978
    • Random House
    • Paperback
    • ISBN: 0394837738
    • ISBN13: 9780394837734



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