In the opening scene of The O Manuscript, Lars Muhl is an aging, washed-up rock star who has been lying in bed for three years. Abandoned by doctors and living alone on an island, a friend gives Muhl the phone number of a 'seer' in Andalusia. After a single phone call, Muhl is back on his feet and a three-year apprenticeship to the seer ensues.

During their time together, the seer challenges Muhl to abandon his old life and initiates him into the mysteries of the Montsegur and the Cathars. When an old manuscript shows up in the mail, Muhl finds himself in possession of the secret history...