Cloud's Rider, Paperback/C. J. Cherryh

On a distant planet, all the native creatures communicate telepathically, projecting images which drive humans to madness. As a result, the people live in walled cities and owe their lives to the nighthorses, equines who can bond with certain riders and provide a telepathic buffer. But one savage winter, young Danny Fisher and his nighthorse Cloud lead the survivors of a deadly telepathic attack to shelter high in the snowbound mountains--only to discover their sanctuary threatened by a vicious predator never before known to humans. Sequel to Rider at the Gate.