"Steve" gains control of the ancient artifact the Negative Black, granting him extreme power. He becomes mutated, and the Negative Black drops from his hands. He no longer calls himself "Steve". He is now Mr. Black and no longer thinks of his friends as friends. He sees them as prey.
You play as Mr. Black, and kill people without getting caught. If you do get caught, it's Game OVER!
You need to move quickly through the castle, and you gain new weopons as you move on.