Then you go OSRS gold outdoors. You'll see the burglar dropped something. Pick this up, and you will see it's a runestone using engravings in a different language. Return to Sarah and give her the rock. She'll say the Black Wizards use these runestones as plans. When you arrive there will be a cutscene with the Dark Wizards speaking with all the Dairy Cow at the corner of this room. The Darr Wizards say they are going to kill the king by giving him poisoned milk.
They say they are going to send him a letter encouraging him with their tower and giving them the poisoned milk rather than the regular milk. You will see them putting the milk on the table and the wizards heading out to give the king the correspondence. Walk inside the tower and then empty the poisoned milk and replace it with regular milk. You'll observe the poison in the middle with only enough dosages to fill up the wizards poisoned milk. Simply take the cows and provide it back to Sarah. Then after that you'll see a cutscene where they wizards are meeting with the king. The wizards will all die from poison, then the King will run out the door back to Falador.
The Benefits are: The Skill to build a Pasture and also a Coop, A recently born calf along with a poultry, 2000 hunter exp and 2000 building exp. In the coop, it will be empty. Build hooks which require 15 wood and 10 nails.
You can build troughs for food and water which each need five wood. The water trough asks a bucket of water, along with the trough necessitates chicken feed that you can purchase from Sarah. You can even buy more chicken. They will ocassionally put eggs in their pins. You might also fill the space with hay, which you can get from Sarah. You have to have 10 piles of hay rsorder for that.