The Thirty-First Of June — John Russell Fearn

There were six people in millionaire Nick Clayton's limousine when it left a country house party to return to London: Clayton himself, and his girlfriend Bernice Forbes; Horace Dawlish, his imperturbable servant and driver; the unhappily married financier Harvey Brand and Lucy Brand; and the tragic socialite Betty Danvers. But neither the car, nor its six occupants, would ever arrive in London. Instead, just after midnight, the car traveled some thirty miles along the country road - and disappeared...