With the alien Dhryn helplessly following an instinct-driven migratory path through the inhabited spaceways-bringing about the annihilation of other races that lie along the star trail they are following-time is running out for all sentient life forms. Only Dr. Mackenzie Connor and her team stand any chance of solving the deadly puzzle of the Dhryn and the equally mysterious Ro. Are the Ro the universe's last hope of halting the deadly Dhryn migration? Or are they something far more sinister? As the only human accepted by the Dhryn as one of their own, Mac perhaps can intervene and open a line of communication to the Dhryn. And her friend and fellow researcher, Dr. Emily Mamani, may prove key to the process, for she is the only human who has survived possession by the Ro. Can these two biologists solve the riddle of the Dhryn and the Ro before their part of the galaxy becomes as dead as the region known as the Chasm?