Winner of the 1956 Hugo is Robert Heinlein's Double Star. For those of you who don't know Heinlein casts a large shadow over science fiction. He has won more Hugos then any other author at 4 and also won 1 retro award. Along with Arthur C. Clark and Isaac Asimov, Heinlein is a pillar of Golden Age science fiction. I love the term "Golden Age" because it is always given years after the fact; long enough afterward for best works to be remembered and everything else to be forgotten. In the case of science fiction, the Golden Age is when the genre came out of the pulp magazines of the 1920s and 1930s and more into the mainstream. This is, if you will, old school science fiction: stories about Mars, men in rockets, and strange aliens.
First and foremost, Double Star was a fun read. The book is narrated in first person by Lawrence Smith aka Lorenzo Smythe aka Great Lorenzo, actor extraordinaire. Lorenzo is full of himself and high sentence, prejudiced against Martian,s and a master of his craft. He also is immensely entertaining and likable. Within the first few pages, I felt I both understood and liked Lorenzo. Sometimes, the first person narrator can be lost in a story and the observations he gives sound out of place for the character. Not here though. At no point does during Double Star does Heinlein lose Lorenzo's voice. The character feels very whole and real, as do most of the characters surrounding him, with the exception of Penny who feels like the obvious romantic interest and just kind of boring.
Lorenzo is hired to take the place of the prominent leader of the Expansionist Party, John Joseph Bonforte. Initially, he just has to impersonate Bonforte during his initiation into a Martian nest, but that's just the beginning. To tell more would give away the plot but it's a fun journey. I wish the ending had a little more force to it though.
The novel is vague on when exactly it takes place. Lorzeno does not talk about much that isn't relative to him as an actor or the politician that he is impersonating. It takes place far in the future, where the solar system is mostly colonized and ruled by a constitutional monarchy based on the Moon. Mars, Venus, and Ganymede are all populated by aliens. It's an interesting universe, and as far as I know, Heinlein never comes back to it.
I would recommend this to any science fiction fan. It isn't the deepest novel or the most innovative but it is a lot of fun.