The Duplicated Man — James Blish

Paul Danton was a member of a subversive political party which had an answer: make peace with Venus. But the only way to peace was through the overthrow of Security. And Danton had found the one weapon which would make Security's fall possible: the long-forgotten duplication machine.

It had been well forgotten, for a machine which could make up to five duplicates of any living person was too dangerous to have around. But now, what if the top members of Security were kidnapped briefly, and then, suddenly, there were five of each? No government could endure such chaos.