Robert A. Heinlein 
Double Star 

One minute, down-and-out actor Lorenzo Smythe was – as usual – in a bar, drinking away his troubles as he watched his career go down the tubes. Then a space pilot bought him a drink, and the next thing Smythe knew, he was shanghaied to Mars.Suddenly he found himself agreeing to the most difficult role of his career: impersonating an important politician who had been kidnapped. Peace with the Martians was at stake – failure to pull off the act could result in interplanetary war. And Smythe’s own life was on the line – for if he wasn’t assassinated, there was always the possibility that he might be trapped in his new role forever!