A warning by an anonymous caller that "nothing is as it seems" sets reporter Jack Flynn on the trail of the truth, a trail that takes him first to a militia compound in Idaho and then to a workingman's bar in Boston before he realizes that the answers are hidden much closer to home. The flaws in the plot are even more glaring considering the paeans to investigative journalism and its heroes with which McGrory seasons his narrative. It wouldn't have taken Bob Woodward or Carl Bernstein 10 minutes of telephone research to conclude what the author requires three-quarters of a novel to figure out. But in an election year when the candidates compete to see who can put the voters to sleep first, The Incumbent may whet the appetites of a few political junkies