Lady Audley's explanation of where George is buried (Situational Irony)
Just before Robert leaves her at the madhouse in Belgium, Lady Audley finally reveals where George's body can be found: at the bottom of the well at Audley Court. This information is what Robert has been searching for for so long. Ironically, however, it actually doesn't bring him any peace, and only creates a new dilemma. Robert has already resolved not to press charges against Lady Audley, because he does not want to cause a scandal. If he has George's body retrieved in order to lay him to rest, a murder investigation will ensue. It seems that the long awaited revelation will actually not make any difference, and George's body will simply be left un-retrieved.
Lady Audley's guilt (Dramatic Irony)
Throughout most of the novel, Lady Audley believes that she is guilty of having killed George. While she is determined to cover this up, it does weigh on her conscience and make her question what sort of person she is. Robert also becomes convinced of her guilt and works very hard to find evidence to prove it. Ironically, however, it turns out that Lady Audley is not actually a murderer, because George survived. She, Robert, and Phoebe all believed that she was more guilty than she actually was.
The secret (Dramatic Irony)
The title of the novel suggests that it is Lady Audley who is keeping the most important secret, and Robert is certainly convinced that she knows the information that will solve the mystery of George's disappearance. While Lady Audley certainly does have a lot of secrets, and has information about what actually happened that day, it is ironically revealed that she herself does not know the full truth. Luke Marks, who seems to be a relatively insignificant character, is the one who knows the more important secret and who, all along, would have been most able to explain the truth of George's disappearance.
George's return (Dramatic Irony)
Robert assumes throughout the novel that solving the mystery will lead to some kind of reunion with George: either he will know where to go to find him, or he will at least be able to lay his friend's body to rest. When George finally does return to England and shows up at Robert's home, he does so ironically for reasons that have nothing to do with the resolution of the case. George just finally got bored and lonely living in America, and decided to return to see Robert. For all of the work Robert has put into solving the case, in theory, he could have done nothing, and George would still eventually have made his way back to him.
