Ultima Underworld: The Stygian Abyss is the first of the Ultima Underworld series. Although the time of the setting is not made clear during the game, it was released between Ultima VI: The False Prophet and Ultima VII: The Black, so it is fair to assume that it occurs somewhere within the 200 year span between those two games. It is one of the first smooth scrolling 3D CRPGs and pioneered many of the technologies that are today seen as standard, such as smooth lighting and an advanced physics engine to calculate motion.
Tha Avatar is awoken by a strange dream warning of danger in Britannia. The Avatar is drawn to Britannia to witness the kidnapping of Baron Almric's daughter. He is caught by the Baron's guards and accused of the kidnapping. The Avatar is sentenced to the Great Stygian Abyss to rescue the Baron's daughter or die in the attempt.