Written by Robert A. Heinlein at the apex of his powers, Double Star is in my view one of his best novels. It takes a fairly well-worn plot – the actor who must, for some vitally important reason, impersonate a famous man well enough to fool that man's own associates – puts it IN SPAAAACE!, and adds in some of the most vivid characters Heinlein ever drew to produce an absolute masterpiece.
Lorenzo Smythe ("The Great Lorenzo") is an actor of prodigious skill and talent but, as we can tell by reading between the lines, so insufferably arrogant about his abilities and so prideful about the way in which he will and will not use them that he has become unemployable; when we meet him, he is literally down to his last coin. Even so, when spaceman Dak Broadbent – mysteriously trying to avoid being recognized as a spaceman – offers Lorenzo a job, Lorenzo recognizes the urgency, negotiates an advance fee, and does so with both an internal monologue indicating what kinds of jobs he believes are beneath him and dialogue which implies he is constantly in demand.
His initial reaction to avoid agreeing to an impersonation job (he feels that acting as a "double" to someone is the equivalent of prostitution, or at least of ghostwriting) and then decision to take the job when he overhears (through lip-reading) his professional capabilities insultingly disparaged, give us a clear indication of his character (and some clues as to just what in his background made him that way.
Then everything goes south when a Martian and a human enter the hotel room Lorenzo and Dak have met in, and a brief, violent fight leaves the Martian, his accomplice, and Dak's friend Jock dead. Now realizing he is caught up in something far worse than he imagined, Lorenzo also has no choice but to escape with Dak… to do a job that obviously is already worth killing over.
I won't spoiler the rest of the plot; suffice to say that it's really well done, including the reason that Lorenzo has to impersonate a particular person (literal worlds may hang in the balance), the arrangements needed to get Lorenzo to be able to play the part well enough, and various edge-of-the-seat moments where we aren't sure that Lorenzo is going to get out of it alive.
Despite his arrogance, Lorenzo is an engaging protagonist; his voice is clear,droll, measured; I always hear it as a tenor voice, tinged with just a hint of upper-crust English accent, just that little bit world-weary and wise. Whatever his failings, Lorenzo does not in fact overestimate his abilities; he demonstrates multiple times that he has incredibly keen perceptions and a preternatural skill at acting and especially at portraying specific roles to perfection. We can tolerate Lorenzo's pomposity because he is a wonderful lens to view the world with… and while the lens may color what we see, it is a beautifully transparent lens indeed.
Heinlein had one of the great gifts of an author: the ability to write convincingly of things whether or not the things he was writing about were true. Lorenzo gives us multiple monologues on the precise craft of a true great actor and impressionist. As a decent amateur actor myself, I find a lot of his stuff – looked at in the cold light of day – to be twaddle. But in-universe it's tremendously convincing and powerful, giving Lorenzo an area of expertise that allows us to excuse some of his behavior and be willing to stick with him through his trials and tribulations.
Lorenzo also develops through the book. Heinlein, at his best, knew very well how to make a hero develop,but Lorenzo is rather unusual in that generally Heinlein started with young people just growing up and learning their place in the world; such characters are easy to show growing up. Lorenzo is a fully adult man with a career who is suddenly thrust into a dangerous game that requires his talents, and this forces him to change in multiple ways.
Other characters, such as Dak Broadbent and Penny Russell, are also well painted, but beside Lorenzo they tend to fade to near-insignificance. That's a pity, in a way, but it really is Lorenzo's show, in more ways than one, so I suppose it makes sense. We're here to watch him put through a wringer and somehow come out of it alive and, maybe, a better man than he was before.
As with many older SF novels, there are plenty of elements that are no longer usable in straight science fiction – native Martians traveling to earth, for instance. The omnipresent smoking of the 1950s is still in full force – even on board spaceships where one would think the air filtration issues alone would prevent it; much of the culture is the same.
At the same time, Heinlein does try to ring in some changes; I was particularly appreciative of his playing around with fashions, so that men wearing ruffled chemises isn't considered so ridiculous that they'll get laughed at in a bar, for instance. Lorenzo apparently wears a cape regularly. A number of the classic SF tropes of the 50s are also present – regular interplanetary flights, nuclear disposal units instead of wastebaskets, ray guns of various types, etc.
One thing that does stand out is that this isn't the same universe, or even a particularly related universe, to those of his juveniles or stories such as The Moon is a Harsh Mistress or Stranger in a Strange Land; it's completely its own universe, separate and independent as far as I can tell from any other Heinlein work (except I suppose from his late period work when he was unifying EVERYTHING, unfortunately).
The ending of Double Star is also unique; I consider it a "good" ending, but there are some bittersweet notes to it which give it an unusual flavor for a Heinlein novel.
I also have to appreciate the almost Asimovian title; such a double pun doubtless would have amused him immensely.
Double Star is one of my favorite Heinlein novels, and despite some inevitable cultural/sexist failings remains a fast-moving, exciting, and intelligent novel today. I strongly recommend it!