Four linked novellas, featuring Jay Score and the betentacled Martian chess fanatics
More classic EFR as the human PoW John Leeming uses a piece of bent copper wire to wage psychological warfare on the enemy, with the help of his Eustace of course...
Next of Kin is an expanded form of The Space Willies, 1958, itself based on the short story "Plus X". Unfortunately the good stuff with the Eustaces doesn't start until past half way through the book, the first half (presumably most of the expansion?) being more conventional "individualist space pilot laughs in the face of authority".
EFR had two main themes: pompous authority figures being outwitted by clever subordinates, and entire alien races being no match for a single canny human. Put the two themes together, and you get the classic Wasp.
Humanity is at war with the evil Sirian Empire: we have the better tech, but they have superior numbers. So, to win, we need to do something cleverer than fight them head on. James Mowry, who can pass as a Sirian, is recruited as a "wasp" -- an agent provocateur dropped behind enemy lines with instructions to cause as much mischief as possible. As the leader and total membership of the otherwise fictitious Sirian Freedom Party, Dirac Angestun Gesept, he causes plenty of havoc.
EFR's writing has aged better than many other 1950s authors, possibly because the fight against self-important bureaucrats is ever more relevant, but his style and the humour is a little old-fashioned. Indeed, although EFR is careful to paint this as the Good Guys desperately fighting lots of Very Bad Guys by any means possible, this is rather harder to read as a comedy today than when it was written. Today we are more used to being the victims of psychopathic terrorists than the supporters of heroic resistance fighters; one's first natural impulse is to identify with the Sirians. However, here (most of) the victims are either nasty criminal thugs, or very nasty secret police (basically just a purple-skinned Gestapo -- indeed, compare the names of the Sirian Secret Police, the Kaitempi, and the Japanense Imperial Army's military police, the kempeitai), so the impulse does not last long. In fact, everyone is a bit of a cipher -- even Mowry careers from one incident or crisis to the next.
Yet, as a dig at totalitarianism, and as a resistance fighter's pocket instruction manual, Wasp still makes good reading.