[Ziggurat]

The King's Assassins: when you first open the King's treasure thing you find out your rating with the Assassins is lowered. A simple plot would to have Assassins guarding the King/Queen area so they would go hostile and make leaving more difficult.

A more complicated plot: you must curry favor with the Queen who you meets in her boudoir, perhaps with a blue flower (or dead frog for a tasty appetizer?) She would tell you of her plan to poison the king. After satisfying her, you have access to the deposit slip in the straw (or she would give it to you). Perhaps she would leave then and get caught by the King's Assassins. They would remain neutral to you until you took the King's treasure (maybe the 2nd or 3rd item?). You would than have to fight your way out by killing all guards or else the castle would go hostile again. These Assassins would be tough. Not sure if I have seen one in the game.