Cover art is whatever (actually I quite like the front cover, so perfectly of its era as it is); this BBCF is all about the copy-writing.
Thanks to Pandemonium Books’ sale on used books for R. W. Mackelworth’s The Diabols (1969), and for one-sentence paragraphs:
Their bodies were colored lights; their voices were music. But whatever they touched was incinerated!
For a moment in time their destructive powers were limited to a small portion of Earth. Yet they were determined to burn the whole planet to a crisp.
Was there no hope for man’s survival?
As a last resort Boraston is projected into a future where the Diabols have almost won. Only a few humans remain, struggling to stay alive by holding the Diabols off with skirmishes and holding actions.
Can Boraston devise a method to destroy them?
If he succeeds, Earth can plan to save itself from the Diabols.
If he fails, Earth was doomed to become nothing more than a charred and blackened cinder in the galaxy!
It makes me unironically happy that someone was paid to write this, and that someone was paid to publish this. What a creature is man.