The Dead Secret is a novel published by Wilkie Collins, first in 1857 as a series in Charles Dickens' Household Words weekly magazine and later the same year as a book.
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.
Sarah, now living under her married name, acts as a nurse after Rosamond's birth, and gives Rosamund a cryptic warning to avoid the room in which the Secret is hidden.
The obsessed and arguably deranged Sarah prefigures the character of Hester Dethridge in Collins's Man and Wife, and more distantly those of Lydia Gwilt in Armadale and the female protagonist of his late novel, The Haunted Hotel.
The Dead Secret was first published serially in Charles Dickens' Household Words weekly magazine in 1857, with 23 installments between January 3rd and June 13th.