The Quadrail series is a sequence of five (as of 2012) science fiction novels by Hugo Award-winning author Timothy Zahn. In a space opera setting, human Frank Compton is hired by the Spiders, servant beings who operate the intergalactic Quadrail network, and their enigmatic masters the Chahwyn, to investigate a group-mind, the Modhri, which infiltrates other sentient beings and controls them either directly, or by subconscious suggestion. Together with Bayta, an enigmatic woman the Spiders have assigned to help him, he researches and combats the Modhri and later its controller, the Shonkla’raa. Source: Wikipedia (en)