Shadow Tower is set on the continent of Eclipse, in the Holy Land of Zeptar. The player takes the role of a mercenary named Ruus Hardy. Returning home to Zeptar, he finds that the entire city, as well as the central tower, have been sucked into the underworld. He meets an old man who gives him the Dark One's sword, the only weapon which can injure the demons responsible. Swearing to rescue the old woman who raised him, as well as the rest of Zeptar, Ruus descends into the underworld.