H. B. Fyfe 
D-99: A Science Fiction Novel [EPUB ebook] 

Five citizens of Terra were being held on other worlds — and the ultra-secret Department 99 existed only to set them, and others like them, free. Chapters alternate between stories of five Terrans being held by the authorities on alien planets and the efforts of a secret Terran government department to come up with plans to free them. In the midst of the planning and problems, a huge power outage causes even more trouble for D-99 as they struggle to keep the trouble from a problematic agent whose previous sufferings cause him to have severe claustrophobia and to react violently from it.