The Spy in Black by J. Storer Clouston

The house of Breck was a mansion of tolerable antiquity as mansions went in the islands, and several curious stories had already had time to encrust it, like lichen on an aged wall. But none of them were stranger than the quite up-to-date and literally true story of the vanishing governess.

Richard Craigie, Esq., of Breck, the popular, and more or less respected, laird of the mansion and estate, was a stout grey-bearded gentleman, with a twinkling blue eye, and one of the easiest-going dispositions probably in Europe. His wife, the respected, and more or less popular, mistress of the mansion, was lean and short, and very energetic. Their sons were employed at present like everybody else's sons, and do not concern this narrative. But their two daughters, aged fifteen and fourteen, were at home, and do concern it materially.