Popular 1862 mystery novel written by Mary Elizabeth Braddon. Referred to as a 'Sensation Novel' in Victorian Literature classes, it portrays the innermost depths of she for whom the novel is named, and her fervent desire, even obsession, to snuff out [[spoiler: all memories of her past life]], as well as he who may have figured out the eponymous secret...
Upon discovering the most exquisite, doll-like beauty of Lucy Graham, Sir Michael Audley, a baronet of Audley Court, proposes to and marries her immediately, and seems to settle into an idyllic life, the jealousy of Michael's daughter from an earlier marriage, Alicia, notwithstanding.
In what seems at first to be the B-plot but very quickly takes the fore, George Talboys returns from Australia, to which he fled for some years to make his fortune, abandoning his wife Helen, who has since had a child. Unfortunately, George discovers that Helen has died, leaving her child in the care of her father, an old drunk who dotes on little Georgey, but is not a suitable guardian. So George makes plans to return to Australia, but disappears shortly thereafter...
Enter the barrister Robert Audley, Michael's brother and George's best friend. Before his friend disappears, he seems to be lazy and ill-purposed, but after the disappearance, his skill and single-mindedness are honed to a razor edge as he inexorably seeks the truth. But, it may be more than he can bear...
!!Has examples of
* AlliterativeName: Protagonist '''A'''licia '''A'''udley.
* [[AliceAndBob Alicia and Bob]]: No, seriously.
* BitchInSheepsClothing: [[spoiler: Lady Audley turns out to be one.]]
* BrilliantButLazy: Robert Audley.
* ChekhovsGun: The well.
* DarkSecret: [[spoiler:Lady Audley left her first family behind to make a new, independent identity for herself, after her husband was presumed dead. Since it turns out he wasn't, this makes her a bigamist.]]
* DoubleMeaningTitle: Lady Audley actually has ''several'' secrets she is concealing, though the ones that the title could most likely be referring to are [[spoiler:being Helen Talboys and being insane]].
* GentlemanDetective: Robert Audley again.
* GoldDigger: [[spoiler: Lady Audley turns out to be one of these as well.]]
* HomosocialHeterosexuality: The HoYay between George and Robert Audley is "resolved" or redirected when Robert falls in love with George's sister, Clara.
* KeepingSecretsSucks: Lady Audley resorts to murder a couple of times in an effort to hide [[spoiler:her bigamy]]. [[spoiler:She does crack eventually, though.]]
* KillItWithFire: [[spoiler: Lady Audley attempts to murder her nephew by setting his inn room on fire and locking him inside.]]
* KissingCousins: Alicia has feelings for her cousin Robert. He doesn't feel the same.
** There is also Phoebe and Luke Marks, though in this case it's the woman who doesn't reciprocate the feelings. She had made a ChildhoodMarriagePromise and couldn't back out of it because the thuggish Luke was the kind of guy who might kill her if she said no.
* TheLadette: Alicia.
* MarySueClassic / PuritySue: Subverted.
* MayDecemberRomance: Sir Michael is considerably older than Lady Lucy.
* NotQuiteDead: [[spoiler:Lady Audley's first husband, it turns out. Since this creates quite the problem for her, it leads to her making sure he really ''is'' dead this time. And even that time, it doesn't stick...]]
* ParentalMarriageVeto: George Talboy's father is not pleased about his son's choice in marriage.
* RichIdiotWithNoDayJob: Robert is actually a barrister but fits this as we never actually see him doing any work. He mostly just sits around.
* SecretChaser: Robert Audley, who goes to extreme lengths to prove the titular character's secret, as he figures out what it is fairly early on.
* SecretOtherFamily: Variation. [[spoiler:While Lady Audley had a child in her previous life whom she left behind when she reinvented herself, it isn't just his existence but the fact she was married at all which she is hiding, since she believes her husband dead and [[GoldDigger wants to marry the rich Sir Michael]]. Once she finds out her first husband isn't dead, she not only has to hide his existence, but kill him to protect her secret (and end her bigamy).]]
* SpiritedYoungLady: Alicia Audley.
* TomboyAndGirlyGirl: Alicia Audley and her stepmother Lady Audley, respectively.
* TwoAliasesOneCharacter: Turns out to be the case for [[spoiler:Lady Audley and Helen Maldon. When she gets sent to the ''maison de santé'' in Villebrumeuse, she also has to take on the name of "Madame Taylor" so that she can never be tied to Audley Court there]].