First published in 1958, The Languages of Pao opens with the assassination of the ruler ("Panarch") of the planet Pao, arranged by his brother Bustamonte, who takes over the throne while implicating his nephew Beran Panasper (the novel's protagonist) in the crime. Cheating death, Beran is taken under the wing of Parafox, head of the Breakness Institute (on the planet Breakness, of course), who also brokers a deal with Bustamonte to create various military and technical castes among the population of Pao in an effort to retailate against the Brumbo Clan of the planet Batmarsh, who extorts "tribute" from the Paoians.
The rest of the novel details both Beran's efforts to get revenge for his father's death and take back Pao (and the throne) from Bustamonte and the Brumbos, as well as focusing on Parafox's use of languages within the social classes of the Paoians to shape and alter their attitudes and sense of identity. This latter plot thread is interesting, as several critics have noted Vance's use of the Sapir-Whorf hypothesis, where a language's structure and grammar influence the perception and consciousness of its speakers. Through the construction of various customized languages, Parafox manages to isolate and divide the various social classes of Pao into three specific separate groups (warrior, technical, merchant), each with their own assigned function and particular skills.
However, Beran (after dealing with Bustamonte) discovers the inherent dangers of this social experiment (the warrior caste, for example, consider themselves to be genetically and intellectually superior to the rest of the population, and aren't afraid to rub that idea in other people's faces) and resolves to reunite the population, as well as settling personal scores. Vance proceeds to wrap things up with a rousing battle sequence in the climax, but some readers may find the subsequent final scene either cleverly satisflying or potentially downbeat. Vance lets the reader make the final call. (I liked it, but also thought it was a set up for a sequel, which hasn't materialized as of this date.)
An exciting and suspenseful novel with an offbeat and original narrative hook (language as a social control and shaper), The Languages of Pao (which you can reserve online from the library here) is well worth your time!