The Butler, Verifying is Chapter 168 of the Kuroshitsuji manga.
Summary[]
Jane manages to free herself from Ran-Mao's grip. However, instead of attacking Ran-Mao and Mey-Rin or even attempting to flee, Jane capitulates as she has come to the conclusion that it is unwise to fight someone like Mey-Rin—someone who does not "weigh life and money against each other." She also says that she will have Chris Heathfield relieve her of her duties.
Sure that she must lie, Ran-Mao proposes to kill Jane, but Mey-Rin holds her back. Their mission only entailed destroying the blood supplies and the enemy's lifelines; as long as Jane stops attacking them, they have, thus, no reason to kill her. Mey-Rin then asks Jane whether she was hired for her nursing or her killing skills. Jane tells her that she was hired for the latter before proposing to tell them everything she knows about Heathfield Manor if they let her go.
Hesitatingly, Mey-Rin agrees, and Jane reveals that she is "a security-guard-and-maid-for-hire" who was employed to watch the manor and make sure nobody finds out about the blood harvesting, an operation which started long before she came to Heathfield Manor. She states that protecting the manor's secret was an easy job until Mey-Rin and Ran-Mao came and that she does not even know why the blood is collected. She only knows that Abbie and the house steward are in charge and the manor is often visited by a group of people in black hoods at night. Abbie would lead them to the basement, and she and the house steward would make sure that the blood supplies are smuggled out of the manor by hiding them in tradespeople's goods.
After Jane told her everything, Mey-Rin turns to Ran-Mao and sees her holding a big piece of machinery that she has ripped out above her head.
Jane wakes up the sleeping maids and tells them to run upstairs before they are hit by Ran-Mao who is savagely destroying the basement with the ripped-out piece of machinery. Scared, the maids hurry out of the basement, and shortly afterward, Mey-Rin comes out of an adjourning room which used to hold the blood supplies. She announces that she has disposed of them all, and she and Ran-Mao happily go to get relieved of their duties as well after having completed their mission.