The Butler, Having a Laugh (その執事、朗笑, Sono Shitsuji, Rōshō) is Chapter 82 of Kuroshitsuji manga.
Ciel Phantomhive is appalled to find that Derrick Arden is in a seemingly fine condition. Derrick approaches Herman Greenhill, again commenting that the tea smells good. He proceeds to viciously bite Herman in the arm, and Edward Midford lunges over and kicks his chin. Derrick recovers, and Ciel and Edward recognize the stitched wound on his forehead, realizing that he is a Bizarre Doll. He peels off his eyepatch and calls for Sebastian Michaelis. While the prefects struggle to restrain Derrick, Ciel orders for his capture.
Sebastian, acting on command, cleanly removes the tablecloth and traps Derrick in it. Afterward, he tends to the grievous injury on Herman's arm. Ciel reveals Sebastian to be his butler, much to the others' surprise. He discloses that the reason he entered Weston College was to find Derrick and the rest of the missing students; he concludes that Sebastian was unable to find Derrick's whereabouts because Derrick was already dead.
Ciel then points his pistol at the headmaster, demanding for an explanation. Edward tells the confused Clayton and Cheslock that Ciel, the Earl of Phantomhive, should not be opposed. Although Ciel is questioning the headmaster, it is Herman who speaks up: he states that he and the rest of the prefects simply wanted to protect the school. For that reason, they had set out to kill Derrick. Fearing that Herman will take the severity of the blame, Edgar Redmond had then proposed an idea to revive Derrick from the dead. Subsequently, the prefects arranged a contract with Rian Stoker, the leader of the Aurora Society and director of Karnstein Hospital, and his research partner.
Sebastian says that he now understands the reason behind Derrick's disappearance; the headmaster, who was able to escape his pursuit; and how these two factors tie into the Aurora Society, which is the association specializing in human regeneration. He figures that the one who has wrapped all of this in such difficult mystery is the individual seated at the head of the table—that is, the headmaster. The prefects assert that the headmaster has nothing to do with it, but Sebastian returns that he is not directly reproaching "the headmaster," but rather the individual who is claiming that title. He then tells the headmaster to drop the teacher act.
A brief pause issues, and then the headmaster says that he actually is fond of his job. He points to Ciel, stating that it was "truly pleasant watching [his] struggle from the grand tier," and that he has offered him the best of laughs. Much to Ciel's shock, he removes his hat and reveals himself to be Undertaker.