Della Wetherby tripped up the somewhat imposing steps of her sister's Commonwealth Avenue home and pressed an energetic finger against the electric-bell button. From the tip of her wing-trimmed hat to the toe of her low-heeled shoe she radiated health, capability, and alert decision. Even her voice, as she greeted the maid that opened the door, vibrated with the joy of living. "Good morning, Mary. Is my sister in?"