It has stronger science fantasy elements combined with a weird Prisoner of Zenda type plot. The book opens with Paul Harrell, a criminal sealed into a stasis coffin, being summoned out of it to Darkover. He is the unique duplicate of Bard di Asturien and has been summoned to provide his duplicate. Bard is one of two leaders struggling to unite the Hundred Kingdoms. The novel covers the beginning of their union under the Compact achieved not by Bard, who is the novel’s principle character, but his rival Varzil the Good.
The book has several very game worthy ideas. The most interesting is the science behind not only the ability to summon Paul but why he had to exist: Cherilly’s law. The law states “Nothing is unique in space and time except a matrix; every item in the universe exists with one and only one exact duplicate, except a matrix stone.” A matrix stone is a stone native to Darkover (but also capable of being created) that amplifies psionic powers. Matrix stones and Cherilly’s Law could be a magical idea that could propel an entire series of adventures or even be a cornerstone of a campaign. Imagine a megadungeon which made prominent use of this principle.
There are a couple of other ideas that jump out at me. Among things in the Compact is the outlawing of distance weapons requiring those who intend to kill to place themselves at risk. The other is the novel recounts the initial interactions between the the Priestesses of Avarra and the Sisterhood of the Sword mentioned in the Hawkmistress entry which leaders to the Order of Renunciations.