Ideas for a plot, please help?

I'm writing a story with witches and wizards. They don't use wands, they have a ring with a gem for the center piece which represents what power they have (red for fire, blue for water, green for wind, brown for earth, black for death, yellow for life and purple for lightning). I've decided that a Death Wizard (Necromancer) who was banished and stripped of power will rise up to take over the world. He has an army of magicians and monsters to achieve this plan. All I need is like a plot (if he achieves this goal, or does he get stopped and his plan is stalled for the time being, ec cetera) and maybe a Magic School. Please don't suggest Hogwarts because I intend to make this very un-Harry Potterish as possible. Please and thank you :)