The starting coordinates are just there for a spot in the village of Biddestone. No need to search there. If you wish to find the 17th Century Elm cottage, it is to the right of the duck pond and shown below. Its the cottage where Agatha Raisin lives 
. Please don't knock on the door, Agatha wasn't there at the time of setting 
The final location can be obtained by completing my Adventure Lab "Agatha Raisin - She's Amazin'". You can find further detail about the App for Adventure Labs here: https://labs.geocaching.com. If you already have the App then search on nearby Adventures to find it.
Direct link to the Adventure
Stroll through the charming village of 'Carsely' looking for clues. Answer the 5 questions in the Adventure Lab and then recheck the journal to be given the final coordinates.
You will be looking for a small camouflaged lock n' lock tupperware box with perhaps room for a small Tb. Please do not leave any raisins
Update June 2022: Following some recent logs mentioning problems with phone network signals, it seems to be different between networks. I've increased the 'ringfence limit' on all stages to 800m as there maybe better reception nearer The White Horse.
New update July 2023 - following a request from Geocaching HQ, the ringfence limit has been set to 500m (new maximum allowed) between stages