Harlan Ellison once said that the best sentence in all of science fiction was Heinlein's "The door dilated" because it packed so much into so little. Double Star is a lot like that, with an action-packed thriller plot surrounded by a mess of fascinating details about the developing solar system and relations between humans and Martians.

The basic plot follows Lorenzo Smythe, an egotistical and underworked actor who finds himself roped into the role of a lifetime, impersonating the great politician John Bonforte for a vital Martian deal, since the real thing has been kidnapped by the dastardly Opposition. One thing leads to another, and Lorenzo winds up playing for far higher stakes than he signed on for. The story is pretty basic, a transition between 'juvenile Heinlein' (Space Cadet, Have Space Suit Will Travel) and 'classic Heinlein' (Starship Troopers, Stranger in a Strange Land). Smythe begins as delightfully weaselly narcissist who develops integrity by playing a man with some, and the supporting cast are some of the best examples of Heinlein's stock square-jawed pilots and uber-competent secretaries.

So about those amazing details. The description of a spaceman's walk and terrible ground clothes that open the book are some of the greatest expository writing in the genre. Martian society is mostly sketched at, but all seems quite consistent for a race that reproduces by budding and holds propriety above all else. Heinlein's politics are too expansive to box in, aside from the basic claim that he loves thinking about them, but this novel is some of his more honest thoughts on politics. Democracy is the worst system we have, except for all the others, and the greatest game of all. There should be a division between the messy business of policy and the symbols of State, so that we can have change with continuity, and one quote which I'll reproduce in full.

"If there were ethical basics that transcended time and place, then they were true for both for Martians and for men. They were true on any planet around any star-and if the human race did not behave accordingly they weren't ever going to win to the stars because some better race would slap them down for double-dealing.
The price of expansion was virtue. "Never give a sucker an even break" was too narrow a philosophy to fit the broad reaches of pace."

Dang, Heinlein, dang.