The secret of the title is the parentage of the heroine, Rosamund Treverton, who has been passed off as the daughter of the wealthy former actress Mrs Treverton of Porthgenna Tower, but is in fact the illegitimate child of her servant Sarah Leeson by a local miner (Mrs Treverton's motive was to provide her husband with a child, being apparently unable to bear children herself). Sarah writes down the details of the secret from the words of the dying Mrs Treverton, and hides the paper bearing the message in an unused room at Porthgenna. Having previously tried my hand at short serial stories (collected and reprinted in _After Dark, _ and _The Queen of Hearts), _ I ventured on my first attempt, in this book, to produce a sustained work of fiction, intended for periodical publication during many successive weeks. The experiment proved successful both in this country and in America. Two of the characters which appear in these pages -- "Rosamond," and "Uncle Joseph" -- had the good fortune to find friends everywhere who took a hearty liking to them. A more elaborately drawn personage in the story -- "Sarah Leeson" -- was, I think, less generally understood. The idea of tracing, in this character, the influence of a heavy responsibility on a naturally timid woman, whose mind was neither strong enough to bear it, nor bold enough to drop it altogether, was a favorite idea with me, at the time, and is so much a favorite still, that I privately give "Sarah Leeson" the place of honor in the little portrait-gallery which my story contains. Perhaps, in saying this, I am only acknowledging, in other words, that the parents of literary families share the well-known inconsistencies of parents in general, and are sometimes unreasonably fond of the child who has always given them the most trouble. -- Wilkie Collins, _January, 1861_