In a long passage, Inspector Bucket informs Sir Leicester Dedlock that his wife is suspected of the murder of Tulkinghorn. He also tells him the sordid story of her lover, Captain Hawdon. Sir Leicester is visibly shaken, and appears to have all the blood drained out of him. He learns that his wife had visited the grave of "him who as should have been her husband," and also that Tulkinghorn knew the secret. Thus the emnity between his wife and his lawyer is revealed -- and the possibility of her having murdered him is given motivation.
The Smallweeds, the Snagsbys, and the Chadbands arrive and tell Bucket that they know of love letters to Captain Hawdon from Honoria. They hope to profit from this somehow, but Bucket dismisses everyone.
Bucket also arrests Mademoiselle Hortense, and we learn of her duplicity in writing letters accusing Dedlock of the crime. Bucket has employed his wife to spy on her, and he has all the evidence, including the murder weapon, to convict Hortense.
Chapter 55 has Mrs. Rouncewell visiting her son in prison. They have not seen each other for many years, and Mrs. Rouncewell and George are very happily reunited. He agrees to defend himself legally.
Mrs. Rouncewell then goes to the Dedlock London house, and tells Lady Dedlock that George is being held for Tulkinghorn's murder. She also shows Lady Dedlock a newspaper account of the murder of Tulkinghorn, with Lady Dedlock's name and "murderess" underneath it. This was the false incriminating letter composed by Hortense.
Mr. Guppy visits and sees Lady Dedlock, telling her that Captain Hawdon's letters were discovered and may soon come out. Lady Dedlock sees no other way out, and writes a letter to Sir Leicester, explaining she went to Tulkinghorn on the night of his murder, but didn't kill him. She admits to her scandalous past, and then she veils herself, leaving her jewels, and flees.
In Chapter 56, after Lady Dedlock's abrupt leaving, Sir Leicester's cousin, Volumnia, discovers Sir Leicester unconscious on the floor of the library. He has had a stroke - he recovers enough to signal for his Lady but he is told she has gone. In an extraordinary example of the power of love, Sir Leicester reads Lady Dedlock's letter and instantly forgives her. He wants Dedlock to find her immediately, and sends the message, "Full forgiveness," to Lady Dedlock. He has not any intention of reproaching her for her past sins, and only desires to have his love and his wife back in his house.
Bucket tells Mrs. Rouncewell that Hortense is the murderer, and that George will go free fully exonerated. Sir Leicester finds Esther's monogrammed handkerchief that Lady Dedlock had kept. He maintains to everyone in the house that he forgives his lady.
Bucket goes to the shooting gallery, and gets Esther's address from the now-freed George. Bucket asks permission of Mr. Jarndyce to bring Esther with him to search for her mother.
Lady Dedlock, inscrutably, is wandering, buffetted by weather, around the brick kilns where Jo had almost lain down to die before Esther took him away.
The resolution of so many loose ends takes place in these three chapters. The Rouncewells are restored to each other, and George to liberty. Sir Leicester learns of his lady's deception, and promptly forgives her. Lady Dedlock flees from the house, and the principle characters are dispatched to rescue her
The reformation of Sir Leicester is rather marked. He has gone from being an object of Boythorn's scorn and hate, to a loving, affectionate, and very forgiving husband.
The coincidence of all three suspects visiting Mr. Tulkinghorn's staircase on the night of his murder would probably not have aroused much suspicion in his reading public. The murder mystery or detective story was not yet common, and such dramatic license was easily accepted in Victoian novels.
Despite Hortense's guilt in the murder, the mystery continues with the pursuit of Lady Dedlock. The clue to her whereabouts is the significant white handkerchief, which foreshadows Lady Dedlock's death in it's previous use as a shroud for a dead infant.
Mr. Guppy is used yet again as a plot device, and he, like Mrs. Rouncewell, gives Lady Dedlock wrong or useless information. She doesn't yet know of Hortense's arrest, nor does she know of her husband's forgiveness. If she had known these things, her death might have been prevented; as is, her ignorance wrenches still more drama out of a dramatic situation, driving her toward death.