The Staying Power of Sir Rohan

A young doctor rides along with an old man of the town, but as the night gets stormy, they have to take refuge at the house of an old lady, where, quite preposterously, they have to tend to a patient and the events take some interesting turns. Who was the patient they were tending to? Why did the horse refuse to move further? Why did the old lady of the house dislike the young doctor? Read the story to find out!