An Invisible Sun :

Set hundred years in the future, history professor Christopher Cousins believes he’s contracted a mysterious plague which is somehow related to the orbital Gates that allow light-speed travel through the solar system. But the governments and corporations of the solar system are willing to do everything they must to suppress the existence of it. What’s more, those with the plague can hear and see strange things no one else can. As he investigates, he falls in with a group of dissidents (or are they terrorists?) who, like him, want to uncover the truth–which may be the biggest secret humanity has ever kept.