Prepare to embark on an adventure beyond imagination with the return of the best selling role-playing series of all time. In the 9th and final chapter in the 20-year legacy you return to Britannia for your last epic quest. As the heroic Avatar, only you can save Lord British and his people from the evil Guardian who has devastated the landscape and tainted the 8 sacred virtues. Valiant combat, magical prowess and knowledge of the 8 virtues are your weapons against evil in Ultima IX: Ascension, the most epic role-playing game ever created for the PC.

In the beginning of Ultima IX, the Avatar had somehow returned to Earth for an unspecified amount of time before getting back to Britannia. The game starts just after the end of Ultima VIII, in which the Avatar is transported to a Guardian-controlled Britannia. He arrives in Britannia on a mountain overlooking the Guardian's keep in Terfin. The Avatar is transported to Stonegate by Hawkwind the Seer (from Ultima IV), who informs him that great columns have appeared throughout the land, and their malignant influence has caused plagues, famine, and other natural disasters. Under their power, the people of Britannia have twisted the Virtues into mockeries of their true meaning. The Guardian is helped by Lord Blackthorn, who leads the Wyrmguards and forces the people to obey the Guardian.

As the quest progresses, the Avatar learns that the Guardian has stolen the Runes of the Virtues and twisted them into the glyphs that form the heart of each of the columns. Most of the game consists of traveling through the dungeons to recover the glyphs and visiting the Shrines of the Virtues to meditate and cleanse them. Eventually, it is revealed that the Guardian is nothing other than the dark half of the Avatar himself, and the only way to save Britannia is for the Avatar to ascend to a higher plane, taking the Guardian with him. The player is able to accomplish this via an Armageddon spell cast behind a Barrier of Life, which takes the Avatar and the Guardian to a higher plane out of Britannia.