Night Train To Rigel

It all starts when a man comes to deliver a message to Frank Compton--only to fall dead at his feet. What follows is a suspenseful thriller that only Timothy Zahn, a master of hard SF adventure, could have written.
More than two hundred years from now, the Quadrail transportation system run by the enigmatic Spiders connects civilizations throughout the galaxy. But someone is threatening the entire system and the worlds it serves with a military force that could wreak interstellar havoc. Worse yet, a more subtle and sinister threat lurks: the Modhri, whose unique coral is prized throughout the galaxy, but which has properties that may create addiction--or worse. Compton, a sharp investigator, lost his job with Earth's security forces when he exposed a corrupt scheme that had roots in high places. Enlisted by the Spiders to find out who's trying to take over the Quadrail, he's got his hands full, because he's got beings of many races gunning for him to keep him from discovering a far-flung conspiracy that could destroy every civilization in the galaxy.
The result is one of Zahn's most memorable and compelling novels in years.