E. E. ‘Doc’ Smith 
The Imperial Stars [EPUB ebook] 

Classic space opera adventure, Book #1 in the ‘Family D’Alembert’ series. The Empire of Earth, spanning more than a thousand solar systems, is threatened by a conspiracy from within. Now, with more than three-quarters of the Galaxy ready to fall into enemy hands, the Empire is forced to call on its top-secret weapon: the renowned Circus of the Galaxy featuring the d’Alembert family, a clan of circus performers with uncanny abilities. But even these super agents may not be in time to save the Empire.