The Categorical Imperative is supposed to provide a way for us to evaluate moral actions and to make moral judgments. It is not a command to perform specific actions -- it does not say, follow the 10 commandments, or respect your elders.
A blurb on a book can be any combination of quotes from the work, the author, the publisher, reviewers or fans, a summary of the plot, a biography of the author or simply claims about the importance of the work.
The best plot twist is an unexpected one. This means something happens that the reader could in no way infer was going to happen, or perhaps a change in the story that might not have been completely unexpected, but occurred at a completely unexpected time in the story.