The Spy in Black by J. Storer Clouston

A procession came down the long slope at the head of the bay. Each vehicle but one rumbled behind a pair of leisurely horses. That one, a car with a passenger and his luggage, hooted from tail to head of the procession, and vanished in the dust towards the pier. The sea stretched like a sheet of brilliant glass right out across the bay and the firth beyond to the great blue island hills, calm as far as the eye could search it; on the green treeless shores, with their dusty roads and their dykes of flagstones set on edge, there was scarcely enough breeze to stir the grasses. "We shall have a fine crossing," said the passengers in the coaches to one another.

They bent round the corner of the bay and passed the little row of houses, pressed close beneath the high grassy bank, and rumbled on to the pier. The sentries and the naval guard eyed the passengers with professional suspicion as they gathered in a cue to show their passports, and then gradually straggled towards the mail boat. But there was one passenger who was particularly eyed; though if all the glances toward her were prompted by suspicion, it was well concealed. She was a girl of anything from twenty-two to twenty-five, lithe, dressed to a miracle, dark-haired, and more than merely pretty. Her dark eyebrows nearly meeting, her bright and singularly intelligent eyes, her firm mouth and resolute chin, the mixture of thoughtfulness in her expression and decision in her movements, were not the usual ingredients of prettiness. Yet her features were so fine and her complexion so clear, and there was so much charm as well as thought in her expression, that the whole effect of her was delightful. Undoubtedly she was beautiful.