A nice little story set in a Cold War diplomatic showdown over a powerful but ruled by a lonely princess.
Modern readers might object that people do not think that way or otherwise argue that the characterization is poor but this is a story written in the early 1960s when people's sense of duty was still strong (the hippies and other radicals were vastly outnumbered by those who did follow their duty). For many people then, and some people now, dying or suffering emotional pain for their country is a perfectly acceptable thing to do if required. That so few books and movies depict that basic reality makes it a relief to find one that is both sensitive to individual thoughts on the border between private needs and public duty and which describes it in a very unemotional manner.
The ending was somewhat too pat but only slightly. The introduction in many ways gave it away. The stereotypes of the Princess and her husband-to-be are likewise predictable as well and only the main protagonists are really well depicted as thinking and calculating human beings (the servant being an alien does not qualify).
In general, the book was a relief to read. A much drier depiction of human emotion is far more enjoyable that people trying to describe it as deeply as possible. The writing was enjoyable, the plot engaging, and the protagonist entirely credible.
Only the ending and the overdone stereotypes of the princess are why it got 4/5 stars. Well worth your time.