This Ace Double, F-149, was published in 1962.
The overall concept is enjoyable - and the two different cultures (the sprawling human empire and the insular aliens) are both brought to life well. Technology is (happily) used to support the story - making this a pleasant change from the 'LOOKIT TEH ATOMICS' school of plotting that permeates the weaker Doubles.
King of the Fourth Planet, by Robert Moore Williams is just a mess.
John Rolf is an exiled human, living midway up a spiritually-significant Martian mountain and, for vague reasons, developing a telepathy machine. The machine brings the attention of corporate raiders (seriously) from Earth, who bring along his daughter as thinly-veiled sex hostage.
Rolf and his daughter fight off the raiders with the help of the native Martian population, who, rather coincidentally, have already mastered the art of telepathy ('the i-being') and use it in wise and mysterious ways. There's no golden thread throughout the story - each scene is driven by technology introduced purely for the purpose of moving the plot (such as it is) along. The combination of Wise Old Martians and the inexplicable (but super-handy) psychic machinery is too much to handle, and Rolf and his kin aren't interesting enough to carry the story on their own.
* A later printing (1981) returned to the original title and increased the length again. DeVet wrote (flying solo this time) a sequel in 1991, called (predictably) "Third Game". For another [better, really] review - check out Rich Horton's work. He's studiously read all the various "Second Game" variants...