How far down the path of dark magic must a man go before he forgets his old morals?

A dragon animated by undeath, but trapped and thus unable to seek revenge on those who wronged it. A young apprentice mage, about to be expelled from his school for his failures. One carries awesome abilities but is unable to utilize it. Another has stagnated and can't see a way to improve. Two beings who should have never interacted with each other.
What happens when, against all odds, the two inexplicably meet and forge a contract?
An agreement is made. The ancient beast will give the mortal a piece of its power, so that he may walk the path to lichhood. In exchange, the mage turned necromancer would build a kingdom of undeath and prepare the world for the dragon's return.