It starts off so simply: Jack, still feeling down after the tragic events of ''Infernal,'' is hanging in Julio's when a regular named Timmy asks him for help. His teenage niece has been missing since this morning; the police say it's too early to worry, but Timmy knows something bad has happened. Jack says he'll put the word out on the street. This innocent request triggers a chain of seemingly coincidental events that lead Jack into the darkest days of his life. As has become evident in the series, Jack has been singled out, unwillingly, as the champion of one of the two supernatural forces contending for control of all human life on Earth. Neither of these forces are good or evil, just dangerous and amoral. They value and notice individual humans about as much as we do mosquitoes. Jack is desperate . . . and the last thing you want to do is make Jack desperate. That's when things begin to blow up and people begin to die. A hang-onto-your-hat-and-heart thriller of triumph and tragedy that barrels along at F. Paul Wilson's trademark breakneck pace.