Shadows of the past - Michael Jan Friedman

Long ago the alien Quistillian leadership ordered its agent, Lucifer, to conquer Earth. The X-Men stopped him, but the victory cost Professor X the use of his legs. Now Professor X claims he has evidence of a massive secret Quistillian invasion plan. To stop it he splits the X-Men into three groups and sends them on urgent missions to hidden Quistillian facilities he discovered, one in the Andes, one in central Africa and one in Antarctica. The purpose is to seize key pieces of alien technology from the scattered sites and assemble that technology into a defense weapon to stop the Quistillian invasion.
But is the invasion a lie? Does Professor X have a different, hidden, agenda? Normal human Jeffrey Saunders seems to have the answers to the troubling questions of Professor X'x bizarre behaviour. But his answers don't make things easier, if anything, they make things worse for the X-Men.

Michael Jan Friedman is the author of more than forty science fiction and fantasy books, among them many Star Trek and Star Trek: Next Generation novels.