The Star Kings by Edmond Hamilton (first published in Amazing Stories, September 1947; published in book form, 1949; reprinted in paperback as Beyond the Moon, 1950)
A by-the-numbers space opera.
A twentieth century hero, pure of heart? Check.
Plot adapted from classic literature, in this case, The Prisoner of Zenda? Check.
Telepathic communications? Check? From a far distant future? Double check.
A mind swap between the hero and a far future scientist? Check.
A galaxy divided into warring empires? Check.
Destruction of the scientist's lab, potentially leaving the hero stranded 200,000 years in the future? Check.
A galaxy-destroying secret weapon, too powerful to be used? Check.
Another secret weapon in the hands of the enemy, capable of destroying star fleets. Check.
Discovery that the hero is inhabiting the body of a star prince, one of only three who have the knowledge of how to use the ultimate weapon? Check.
A romantic "quadrangle" between the hero, the future scientist/prince, the woman he (the f s/p) is to marry for political purposes, and the woman he (again, the f s/p) really loves? Check.
A royal assassination, pinned on the hero? Check.
The hero unsure whether the body he inhabits is that of a traitor? Check.
Space battles? Crash landings? Kidnappings? Hopeless situations? Check.
A final blaze of glory and a possible happy ending? Of course.
All of this wrapped up in a glorious science fictional pulp style and transformed beyond the mundane by the skill of the author. Hamilton has taken normal tropes and injected a pulse-pounding narrative that places The Star Kings well beyond the typical space opera*.
I willingly admit that I am a sucker for much of Hamilton's writing. For those familiar only with his juvenile tales of Captain Future or with his writing for comic books, Hamilton's mature works will come as a pleasant surprise.
* Hamilton returned to the worlds of the Star Kings in 1964 with the story "Kingdom of the Stars," Amazing Stories, September 1964, followed by "The Shores of Infinity," Amazing Stories, April 1965. At the request of a French publisher, Hamilton then wrote "The Broken Stars" and "The Horror from the Magellantic" to allow all four stories to be included in Retour aut etoiles (1968); these stories were later reprinted in English in Fantastic, December 1968, and in Amazing Stories, May 1969, respectively. The entire French collection was reprinted as Return to the Stars, 1969. Hamilton also wrote the story "Stark and the Star Kings" with his wife Leigh Brackett, bringing together the Star Kings with Leigh Brackett's hero, Eric John Stark, for Harlan Ellison's never-printed anthology The Last Dangerous Visions; this story was finally reprinted in Haffner Press' collection Stark and the Star King by Edmond Hamilton and Leigh Brackett in 2005 (an earlier -- 2004 -- French version of this title has differing contents). "Stark and the Star Kings" marks the only time Hamilton and Brackett officially shared a by-line.