The narrative resumes with the insertion of Fosco's confession. He proclaims his love for Marian, and explains his role in events. When he and Sir Percival were living together at Blackwater, it quickly became clear that they both needed money. Fosco also learns that some sort of secret threatens Percival, and that it seems that Anne Catherick is in possession of this secret. When he learns of the resemblance between Anne and Laura, he hatches a plan to switch their identities, trapping Laura in the asylum, and giving Percival access to her fortune. By keeping watch, Fosco eventually runs into Mrs. Clements, who innocently leads him back to Anne. Fosco uses his knowledge of chemistry to give Anne drugs to make her appear as though she has regained strength, and encourages Mrs. Clements to take her to London as soon as possible. Although Mrs. Clements has agreed to send her address to Lady Glyde, Fosco has her followed and spied upon by the Countess to ensure that he knows her whereabouts.
Next, Fosco secures lodgings in London and visits Mr. Fairlie to get the letter encouraging Laura to come and see him. Fosco also works with Sir Percival to get everyone out of the house except for the one loyal maidservant, and Madame Rubelle. In the middle of night, while Marian is sleeping, they move her into one of the obscure bedrooms in an unused part of the house, where she is tended to by Madame Rubelle. The next day, Fosco and the countess leave, with the letter from Mr. Fairlie given to Percival, ready to be used to induce Laura to travel to Limmeridge House. Fosco and his wife now travel to Mrs. Clement's s house, where the latter is distracted by the countess. Once she has left Anne unattended, Anne is lured out by a message that she has been invited to spend the day with Lady Glyde. In the cab, Fosco charms Anne, but once she arrives at his house and finds herself alone with him and the Countess, she becomes so agitated that she goes in to convulsions.
Fosco immediately sends for a doctor, but is worried that Anne will die before Laura arrives. He tries to expedite the plans for Laura's arrival, but Anne does indeed die abruptly on July 28, before Laura's arrival. This is especially problematic because the doctor, trying to be helpful, has already recorded the death of the woman he believes to be Lady Glyde. With no other choice, Fosco goes to the station to meet Laura, bringing with him the clothes Anne had worn when he abducted her. He reassures Laura with news of Marian, and takes her to his supposed home, which is actually the home of Mr. Rubelle. He has her examined by two doctors, who declare her insane, and then keeps her sedated until he can transport her to the asylum. He has switched her clothes so that she arrives dressed like Anne, and is taken into custody. Meanwhile, the death of "Lady Glyde" is made public, and she is taken away for burial. Fosco ends his confession by explaining that the countess went along with all the schemes because of the high expectation of loyalty and support placed on English wives. He admits that if Anne had not died at the convenient time, he would have killed her himself, but insists that he has not done anything seriously wrong because he in fact went to great pains to avoid simply murdering Laura outright.
Having finished reading the confession, Walter leaves the house and goes to the cab company that had been hired to drive Laura and Fosco from the train station, where he secures further evidence confirming the date of her arrival. The next day, Laura, Marian, Walter and lawyer Kyrle all travel to Cumberland where Walter meets with Frederick Fairlie, confronting him with all the evidence. Mr. Fairlie finally concedes that Laura is his niece, and still alive. Walter makes a simplified version of the conspiracy public so that Laura's identity can be re-established and has the inscription on the grave changed.
A short time later, Walter travels to France on art-related business, accompanied by Pesca. While they are there, Pesca receives news that seems to distress him, and he asks to go back to London as soon as possible. Before they depart, Walter decides to do some sight-seeing and while passing by the Paris morgue, he hears talk of the body of a very fat man with a strange mark on his arm. He goes inside, and confirms that the body is that of Fosco, who was tracked down by the Brotherhood and killed. Walter confirms that since Fosco's death, the countess has been living near Paris and honoring his memory.
The following winter, Laura gives birth to a son. When the infant is six months old, Walter returns from a short business trip to learn that Frederick Fairlie has died abruptly. Laura and Walter's son is now the heir of the estate and with Marian, who has remained living with them, the family looks forward to a happy and prosperous future.
Fosco's confession is necessary to finally give a complete account of the conspiracy from start to finish. It fills in any lingering questions and makes it clear just how meticulous the plot was. Even with the serious complication of Anne's untimely death, Fosco is able to cover all the tracks. It is almost impossible not to admire the complexity and cohesion of the plot, which corresponds to the ambivalence Fosco has always inspired. He is both despicable in his amorality and alluring in his brilliance.
Fosco's inglorious death thus might almost be met with regret. With the confession in hand and him having fled England, he does not seem to pose any threat. His death serves as a reminder of the dangers of being too proud and of the fact that in the end he was not as all-powerful as he believed. The grotesque spectacle of his body being displayed at the Paris morgue serves an embarrassing and undignified end for such a proud and brilliant man, showing him finally humbled. Fosco's death again combines the satisfaction of a villain being punished for his crimes with Walter being innocent of any violence or bloodshed.
With all of the evidence in hand, Frederick Fairlie comes around to acknowledging who Laura truly is. He does so more out of his exhaustion than any true conviction, showing that he is ultimately still weak and selfish. The presence of Walter as Laura's husband, who now has the legal right to advocate for her and pursue her claims, also seems like it might be an influencing factor. Ironically, Laura's triumph is presented as more of a victory won by Walter, and to a lesser degree, Marian. The change of the inscription on the tombstone marks the final time a written document is corrected to reflect the truth. At last, Anne Catherick will have the peace and respect that she could never find in life.
The conclusion marks the triumph of a new era and a potential set of new values. In contrast with Laura's marriage to Percival, her marriage to Walter quickly leads to the birth of a healthy son. This furthers a reading of Walter as bringing a healthy virility that the aristocratic males of the novel (none of whom father children) do not possess. Not only do Laura and Walter have a son, ensuring future generations, but that infant quickly becomes the heir to Limmeridge House when Frederick Fairlie dies. This signals that the era of the decadent, effeminate aristocrat is passing away in order to be replaced with men who distinguish themselves with their intelligence, courage and integrity. Although not a gentleman by birth, Walter has proven himself the true gentleman of the novel over and over again. Lyn Pykett agrees that "when the three return to Limmeridge House at the end of the novel, they can be seen as replacing an outmoded aristocratic world" (p.104).
Finally, while the happily married couple and their child seems like a very traditional ending, Marian's presence offers an unconventional twist on the family structure. It is very clear that she is extremely important to both Walter and Laura, and that she is an integral part of their family. She offers a balance of masculine and feminine qualities that complements both of them, and together the three individuals look forward to a long and happy life; according to Carolyn Devers, "providing a masculine companion for Walter and a feminine one for Laura, Marian is a full partner in this marriage of three" (p. 115).