Murray Leinster 
The Invaders [EPUB ebook] 

It started in Greece on the day after tomorrow. Before the last act raced to a close, Coburn was buried to his ears in assorted adventures, including a revolution and an invasion from outer space!
We’re not given to throwing around the word ‚epic‘ lightly, but here is one! Swashbuckling action, a great many vivid characters, and a weird mystery—all spun for you by one of the master story-tellers of our time.