The Dedlocks are in London, and Lady Dedlock is in her sitting room with Rosa. She calls Rosa to her side and tells her that she has brought much comfort to her life. She then tells Rosa that she must leave her service. Rosa begins to cry but Lady Dedlock says that she wants her to be happy, and that this is why she plans to send her away.
Lady Dedlock is afraid that, if her secret gets out while Rosa is her maid, that the girl will be tainted by the scandal and will be unable to secure another position in the future. Lady Dedlock genuinely wants her to be happy and safe and so sends her away.
Not long after this, Mr. Rouncewell arrives and Lady Dedlock informs him that he must take Rosa away because she is still in love with his son. Mr. Rouncewell is clearly offended by Lady Dedlock’s haughty tone but restrains himself as he leads the sobbing girl away. Mr. Tulkinghorn is present during this interview and lurks silently in the corner of the room.
Lady Dedlock hides her real motive for dismissing Rosa by pretending to look down on Mr. Rouncewell’s son and dislike his engagement to Rosa. She knows that Mr. Rouncewell already believes she is haughty and cold and, therefore, plays up to this image to protect Rosa.
Sir Leicester goes out on government business after dinner and Lady Dedlock is left alone. Mr. Tulkinghorn comes to see her and tells her that she has broken their agreement and is, therefore, not to be trusted. Lady Dedlock asks what he means and Mr. Tulkinghorn replies that she agreed to take no action regarding the secret, but that she has acted by sending Rosa away.
Mr. Tulkinghorn immediately finds an excuse to blame Lady Dedlock for her own exposure. He implies that she has broken their agreement by trying to protect her maid.
Lady Dedlock understands that this is a warning to her, and that Mr. Tulkinghorn now intends to reveal her secret. She asks him when he plans to do it, but he refuses to tell her and says that he is going home. Lady Dedlock sits in stony silence as he leaves the room. On his way out, Mr. Tulkinghorn stops and looks at the clock in the hall. He reads the time on it, but the narrator suggests that it should spell out the words, “Don’t go home.”
Mr. Tulkinghorn plays with Lady Dedlock and deliberately keeps her in suspense so that he feels she is in his power. The reader is told that something bad is going to happen to Mr. Tulkinghorn when he arrives home.
Lady Dedlock leaves her home by the back door and takes the key from the servant who lets her out. She says she will walk for some time in the gardens. It is a bright, moonlit night. Elsewhere, in the moonlight, Mr. Tulkinghorn crosses his courtyard and makes for his wine cellar. A gunshot rings out in the silent city night. The clock strikes 10 p.m. In Mr. Tulkinghorn’s study, the Roman Allegory points to the same, eternal spot on the floor.
Dickens connects the image of Lady Dedlock leaving her home to Mr. Tulkinghorn returning to his, leading readers to wonder if Lady Dedlock is a murderer.
The next morning, the cleaner enters and runs out of the room screaming. People rush in and out of the room and wish that the Allegory on the ceiling could reveal what he has seen. There is a bottle of wine upon the table and two candles which were blown out soon after being lit. There is a stain upon the ground, and the figure of Allegory has a mad look as it points down at it. The Allegory is the only witness; beneath him, Mr. Tulkinghorn lies face down upon the carpet, with a bullet in his heart.
There are no witnesses to Mr. Tulkinghorn’s murder, except the painted figure on the ceiling, Allegory, which has cropped up several times throughout the novel. It seems that the murderer blew out the candles, either after the murder or to commit the murder in the dark.