Meet King Ono, ruler of Square land, beloved by all. That is, apart from his arch enemy Lord Void, who will stop at nothing to dethrone him.
The King lacks any meaningful construction skills so he needs you to build his castles for him, using nothing but the latest in cutting edge building materials including.. wood, stone and ... iron. You had better make them strong and sturdy too, because Void's loyal, cannon wielding minions will do all they can to destroy them, and send your King tumbling down to the cold, hard ground.
Protect the King's gold coins and gunpowder stashes and he will reward you, but if he suffers because of your inadequate castle building skills he'll wuss out and surrender, or even worse.. die, meaning you'll see none of those glorious shiny things.
Oh.. and whatever you do, be sure to keep those gunpowder barrels out of sight from the attackers, or your king will be taking a royal flight.