Dr. Ramsay lived at the north-country manufacturing town of Whinburn, a prosperous but bleak corner of the kingdom, where smoke had stunted the trees and soiled the herbage, where flowers were scarce and bloomed late, and winter stretched its icy fingers well into autumn and spring. The house, like most doctors' houses, was on the main high road, and part of the garden behind had been turned into a garage, so there was very little room for the bed of bulbs and the perennial border upon which Mavis concentrated most of her outdoor energies. She toiled hard to have a floral display in the summer months, but it was disheartening work, for the frost always killed her wallflowers, and only the hardiest of plants would consent to make a sulky struggle against the smoky atmosphere that seemed to blight the very heart of vegetation and turn the choicest bedding varieties into sickly specimens. Merle, less deeply wedded to nature, had long given up gardening as a bad job, and had handed over her patch of unkindly northern soil to her sister. She was more interested in the car: she liked to watch the chauffeur clean it, and the high-water mark of her bliss came on the days when, on a quiet road and with no policeman within sight, her father would allow her for a brief space to assume command of the driving-wheel. "I'll be your chauffeur, Dad, when I'm old enough to leave school," she would assure him airily. "I _do_ think you might get me a driving licence now! Too young? What nonsense! We've no need to tell the Government I'm only fourteen. I'd soon drive as well as Greenhalgh if you'd let me try. I'm not afraid of anything." "I dare say not, but think of _my_ feelings with a harum-scarum like you at the helm!" her father would reply. "You'd soon collide with a lorry, or land us in the ditch. I'll stick to Greenhalgh, thank you. He doesn't want to run at forty miles an hour." "I'll take proper motoring lessons when I've left school," Merle would declare, "then I'll be ready to drive any car in the United Kingdom--that's to say, if I haven't made up my mind to be a lady detective." Mavis, who was in bed when our story begins, weathered her December attack of bronchitis and came downstairs in time for Christmas Day, but with such white roses in her cheeks that her father looked at her anxiously, and called Mother into the consulting-room for a private confabulation, the result of which was a long private letter addressed Dr. Tremayne, Durracombe, Devonshire, which was posted without the girls' knowledge. Several other letters followed, and the brisk correspondence had just reached a satisfactory conclusion on a certain January day when Mavis, with a shawl round her shoulders, was peering out of the window at the flying snowflakes.