The author examines in fascinating detail the discrepancies between dates in assorted calendars - the intercalated pre-islamic, the Hijri, and the Julian calendars - and the days of the week ascribed to different events in the sirah of the Prophet (saw). He painstakingly relates them to the different theoretical attempts evolved by scholars to try to make sense of the contradictions, and then makes an utterly compelling case for the one system that makes rational sense of all the data.