The Duke's Castle Quest is a series of five goals which stands at the end of the map related goals in the English Countryside. The goals are:
- Cream of the Crop (harvest the dairy farm once; harvest 25 plots of red current; get 2 ice cream cones from friends)
- Perfect Preparations (harvest 100 plots of bluebells; get 3 glasses of grape juice from friends; make barley crumpet recipe once)
- Parting Gifts (get two presents from friends; place one lamb; harvest 25 plots of black tea)
- Once Around the Farm (get two airship patches; harves 25 plots of black tea; make rosehip tea recipe once)
- A Great Start (get six donation cheques from friends; get 15 bushels from friends; harvest 200 plots of cara potatoes)
After completing all of the goals, the Duke's son Henry and Lucy get married. The effect on the game is such that one can trade items between the English Countryside and the Home Farm.