A woman at the very height of society, Lady Dedlock is a master of self-possession and poise. However, her world is turned upside down when the secret engagement and pregnancy of her youth are uncovered.
So here's a good way to try to imagine Lady Dedlock's social status. Picture a cross between a beautiful celeb of the moment (maybe Angelina Jolie), a wife of a wealthy conservative politician (we'll throw out Cindy McCain), and a top style-setter (hmm... how about Sarah Jessica Parker?). Lady Dedlock is at the height of London's social circle: her comings and goings and parties and outings are unfailingly reported in the style section of the newspaper; her houses and clothes are impeccable and deeply envied; and her husband is a rich and powerful man who takes his position in the world extremely seriously.
Now let's try to picture her inner life and thoughts. As a young woman, she had a stillborn baby – so she thinks. Not only that, but her first fiancé drowned. That's pretty traumatic right there, but added to the mix is that she had this baby outside of marriage – a huge, horrible no-no back in those days – and cannot ever let anyone know about it.
Then, added to this trauma and secrecy, she gets the shock of her life when she discovers two guilt-inducing things: 1) her fiancé actually survived, lived in abject poverty, then overdosed on opium, and 2) her baby survived too and was raised in secret by her own malicious and vindictive sister!
OK, so what's the tally? Trauma, secret-keeping, shock, guilt, and – as the final twist – fear. Lady Dedlock realizes with terror that the family lawyer is uncovering all this stuff and at any moment will out her to her husband and destroy all their lives.
So how does she deal? Repression, repression, repression. She turns herself into an almost completely artificial creation, acting out the part of a sophisticated, worldly, and bored elitist. Her every action, movement, and bit of conversation is practiced and calculated. We could say that she is a consummate actress – so skilled that not a single person around her ever suspects anything is wrong. Or we could even call her a work of art, a sort of walking portrait of a member of the nobility. This may be why she's often described as looking at herself in a mirror, and why many of the other characters interact almost interchangeably with her and her portraits (think Guppy and the portrait in the tourist part of Chesney Wold, and Sir Dedlock going to bed near a portrait for his eyes only in his bedroom).
Ironically, it's this constant indifference that raises Tulkinghorn's suspicions in the first place. Lady Dedlock has an amazing ability to repress emotions, but she's not a robot. When she recognizes her fiancé's handwriting on a legal document, she suddenly starts acting all interested and curious – two things that she never allows herself to be. Seeing this strange concern about the handwriting from someone who usually doesn't seem to care about anything and who generally carries herself with a been-there-done-that attitude is so unusual that Tulkinghorn immediately starts investigating.Timeline