The Butler, Appraising is Chapter 157 of the Kuroshitsuji manga.
Years before, in 1877, a pair of street boys approach two rich women and ask one of them if she has any change to spare for them. Seeing their miserable state, the woman takes out her purse and is about to give them some change when her earring suddenly falls off. The boys quickly grab it and run away to Mey-Rin who poses as a boy called "Rin" and is waiting for them on a roof.
Mey-Rin and her parents came to England on a tea clipper, but when her parents died in an epidemic, she was left to live on the streets. She eventually met Jan and his younger brother Hao and, in consideration of her special eyesight, they developed a stealing technique: Jan and Hao approach rich-looking women so that they stop walking and Mey-Rin can shot down one of their earrings with a slingshot from a faraway roof.
They sell their newest conquest and go to a bakery. And because Mey-Rin expresses her wish to eat meat again afterward, Jan plans to go after "something big."
Sometime later, Jan and Hao approach a woman in front of the Royal Opera House, and Mey-Rin gets ready to shot down her earring when something happens.