"Here's a letter for you, Doctor Mack," said the housekeeper, as she entered the plain room used as a library and sitting-room by her employer, Doctor Ezekiel Mack. "It's from Walter, I surmise." This was a favorite word with Miss Nancy Sprague, who, though a housekeeper, prided herself on having been a schoolmistress in her earlier days. "Indeed, Nancy. Let me see it. Walter is really getting attentive. His last letter came to hand only two days...