"What are you waiting for, Doris? You've been hanging on that gatepost all afternoon.""Marshmallow" Mallow, a chubby, pleasant-faced youth flung away the core of an apple and came slowly down the walk toward the girl he had just addressed."Oh, I'm waiting for the postman," Doris Force, an unusually pretty miss of sixteen, tossed carelessly over her shoulder as she continued to gaze down the street. "He just turned the corner.""Must be you're expecting a very important letter," Marshmallow drawled. "I'll bet it's from Dave!""Oh, go eat another apple!" Doris retorted goodnaturedly. "I'm looking for a letter from Kitty Norris, my chum at boarding school. I'm anxious to find out what she's planning to do this vacation.""It's sure going to be dull here at Chilton this summer."