Orcish invasion.

You're right about the Orcs, but I don't know any scripts that would keep the Orc hero in his city until a certain point, so I just blocked all the passages for him.

If you want the enemy hero to stay in the castle and not move, you can write: EnableHeroAI('enemy hero name', nil). Then the hero won't move from his spot. To keep him in the castle, place him there in the city's properties in the editor. ;)