Prerequisite: must have already had the intimidation skill.
(necromancers or anything else with animate dead.)
to get storm the castle you must first get wanted in a city or military stronghold where they would have a bounty on your head. You must then get at least a hundred zombies ( at least two have to be ogre zombies) or skeletons and take over the stronghold or city and take residence in the area for at least one month and have a secured control over the entire area.
you will get; zombies will never leave your command if you summoned them, a higher bonus in intimidation, and one more third level spell slot.