Ellis Peters started it with her Cadfael novels. Derek Jacobi played him admirably in the televised versions but Michael Jecks has to be the master of the medieval mystery.
I have to say Doherty is not one of the best authors in this genre.IMHO.
Used to read his books avidly. Loved his medieval mysteries and Brother Ethelstan stories. Also writes under the names of Paul Harding and Michael Clyne.