The Butler, Under Arrest is Chapter 144 of the Kuroshitsuji manga.
Fred Abberline tells Ciel that he has to come with him to Scotland Yard as he is the prime suspect in the Sphere Music Hall serial murders. Ciel agrees to it, and Fred says to Sebastian that he has to come as well as he is always with Ciel. Fred handcuffs on Ciel, and Finnian interjects that Ciel is innocent and there has to be a mistake. Before he can further intervene though, Baldroy stops him and asks who is going to pay them now. Sebastian replies that his pay has to wait, but he can "come and collect it later."
After sending Ciel, Sebastian, and Blavat to Scotland Yard, Fred wants to turn his attention to Grelle and Othello, only to realise that they have "vanished" without anyone having noticed it. Immediately, police officers start searching for them. In fact, Grelle and Othello are still present; they have only made themselves invisible for regular humans.
Again, Alexis asks "Ciel" if he could explain the situation to him. "Ciel" answers in the affirmative and instructs Tanaka to bring Alexis into the drawing room and make fresh tea. Then, Alexis tells Elizabeth to please return home. Elizabeth is about to say that she cannot, but "Ciel" assures her that he is fine now and she is free to go home.
Edward goes home with Elizabeth, and in the carriage, he asks her if she is hurt and why she did not tell anyone that "Ciel" is alive. Elizabeth then admits that, for all these years, she had never noticed that the boy who returned was not her actual fiancé even though she was always talking about how she was looking forward to becoming his wife and how much she loved "Ciel". If "Ciel" had never returned, Elizabeth says, she would have just married Ciel and spent her entire life with him, never figuring out the truth.
There were days when she had suspected that something was not quite right, but she had never once thought that Ciel was an impostor. And when "Ciel" came back, it threw her into despair. How could she have mistaken someone else for her fiancé? What kind of fiancée did this make her?
For a while, Elizabeth accused Ciel of mocking and hurting her like this. How could he have been so cruel to her? But then, she realised that she was even worse than him as she thinks that if Ciel had never lied about his identity, she would have most likely wished that "Ciel" had survived instead.
Crying, Elizabeth runs into Edward's arms who is quite overwhelmed by everything. While he speaks to God about the "terrible ordeal" with which He tasked Elizabeth, she thinks that her love towards both Ciels had always been a lie.