From the Introduction:
It is a feature of old school RPGs to offer a range of new character classes to supplement the basic ones that appear in the core rulebook. I don’t see any reason not to go along with this tradition and I therefore present the following classes for you to consider for your own campaign: Dervish, Gallowglass, Goliard, Knave, Marksman, Lore Warden, Spellsword and Witch/Warlock.
If you'd like to add further classes, you can readily adapt the ones that appear in Medieval Mysteries. You can even take classes from other class-and-level based games and tweak them to suit.