Delia was a horse owned by William Drummond. She was a gentle, strong mare who liked apples, pulled a dairy cart during Will's rounds and had been treated for the colic by Amy and Alex's dad.
Delia became quickly friends with Denmark, and although she was not known to speak out loud, was able to communicate with the labrador. Delia's hooves were useful during the search for he second clue at Chapelvale's station. The intelligent mare also apparently suggested to Den that she could be used to move the large millstone on Eastpath and uncover the buried armpiece which contained the deeds of the village.