The plot covers about 200 years of history, as Commander Spock picks up Captain Kirk's departing challenge to change his Empire. Other reviews (elsewhere) suggest you read some of the other Mirror Universe and New Frontiers series to appreciate the actual story. NOT me. It's been more than 15 years since my last Star Trek novel. However, book hops through time, dropping in on events that change the Empire - something akin to Herbert's original Dune trilogy in Spock's planning, execution and consequences.