William Riker is now a rear admiral, as a result of the events of last year’s “The Fall” novel storyline — and we’ve confronted him immediately with the sort of diplomatic mission that we often saw driving Captain Picard to distraction. Riker knows well how these kinds of missions go — and makes every effort to not have his own attempt go the same way. But sinister forces are at work, drawing upon the legacy of the past — and Riker finds himself confronted with a much different kind of challenge. How do you settle a dispute between warring parties — when one of them has simply disappeared?