Good Condition for Vintage Sci-fi! Xanth #6.
Night Mare centres around Mare Imbrium, one of the night mares charged with delivering bad dreams to the people of Xanth. Imbri carries half a soul, her fee for carrying Chem Centaur out of the void in the previous book. She is unwilling to relinquish her soul, though the conscience that comes with it impedes her ability to deliver bad dreams. The Night Stallion, ruler of the gourd realm, makes Imbri the liaison to the day and night world and sends her to meet Trent, King of Xanth, with the ominous message, "Beware the Horseman".