In ages long past, the Master taught you the dark secrets of undeath. You could no longer perish, and as long as you had fresh body parts available, neither could your loyal servants - who were coincidentally made somewhat more loyal by the zombification process. But now the Master has fallen! ...Again. And this time those vile heathens have taken the inconvenient extra precautions of separating and inhuming some integral pieces of his unliving remains.
In these dire times, one has to look after his own, and you're a necromancer who is more dangerous than most; you're a necromancer with a business plan. Your zombies will dig up graves and loot valuables, and while they're at it, they'll grab fresh body parts so you can make more zombies to dig up more graves. Sounds good, right? Unfortunately, it's so good that other necromancers are after the same cemeteries you are!