My idea is:
Jack of blades died long ago in fable 1 and his mask destroyed BUT he had a second mask that he created especially so that once the first is destroyed it will start regenerating jack of blades's body years pass and in that gap fable 2 takes place after fable 2 the process completes and jack of blades is back. He starts bulilding an army in secret and gradually get his powers back then of course theres the hero who is the son/daughter of sparrow. you sart in a training session in witch sparrow teaches his son/daughter how to fight using strengh, skill and will. At the end of the session theresa appears and foretells an attack from a powerful warrior (Jack Of Blades) then of course there is a cutscene of jack of blades and a pack of summoners heading for the village theresa takes you away and sparrow is captured by jack of blades you are taken to scythe and he trains you to become powerful then through the game your main quest is to find and destroy jack. you get to jack at the end of the game and he fights with sparrow sparrow gets into a deadly position and now is the final choice to kill jack or sparrow if good jack if evil sparrow if you choose good then you fight with jack if evil then with sparrow, sparrow retires after beating jack if you chose good or you join jack and take over the world if you chose evil. The End, after there will be side-quests like assist jack in killing some guards in bowerstone or training some banshees to fight in jack's army plus somewhere in between the game you will fight scythe (if your evil)