The Butler, Careless is Chapter 160 of the Kuroshitsuji manga.
On a train transporting pigs, Mey-Rin travels to Phantomhive Manor to assassinate Ciel Phantomhive. While travelling, she recalls her briefing with Haku: As there are no pictures of Ciel and as he seldom attends social gatherings, all they know about his appearance is that he is a child with an eyepatch. Also, some months ago, an enemy organisation stormed Phantomhive Manor; the raid was unsuccessful as all members of this organisation were annihilated. This implies that many private warriors must be in Ciel's employ—private warriors which will not be a problem for Mey-Rin as she will shoot Ciel from a great distance. Furthermore, Haku told Mey-Rin that, if she could not kill Ciel, she would lose her position in Qīng Bāng.
From a hill miles away from Phantomhive Manor, Mey-Rin watches and studies the activity on the manor grounds. To her surprise, barely anyone seems to be on the estate—and then, Finnian enters the vegetable garden, followed by Sebastian. They inspect the peas, and Mey-Rin wonders where Ciel and the alleged "private warriors" are.
A week passes and Mey-Rin still has not spotted anyone else on the manor grounds beside Sebastian, the butler, and Finnian, the gardener, which means that nobody except them and Ciel seem to live at Phantomhive Manor—a circumstance that does not make sense to Mey-Rin due to the estate's huge size.
A messenger from Qīng Bāng, Dove, approaches Mey-Rin and comments on the fact that she still has not killed Ciel yet. Dove also informs her that Lau has left Marseilles and that he will arrive in Great Britain in approximately three days. Mey-Rin tells him that he should just give her the food he brought her and leave.
From observing the manor for three days, Mey-Rin noticed that every day at exactly 8 a.m., the curtains of the corner room on the second floor open which means that this must be Ciel's bedroom. She plans to shoot Ciel the next day after Sebastian opened the curtains.
The next day, Mey-Rin readies herself a few minutes before 8 a.m. and waits. Meanwhile, Sebastian enters Ciel's bedroom with his morning tea, wakes him up, and opens the curtains. Ciel wakes up and stretches himself while asking what today's tea is. From her spot on a tree, Mey-Rin spots Ciel and fires her rifle at the same time as Sebastian lifts the teapot. Sebastian deflects the bullet with it, and Ciel jumps to the side.
Mey-Rin is momentarily stunned that she missed, but is then quick to escape. At the same time, Sebastian pours Ciel a cup of tea through the hole the bullet made in the teapot and informs him that today's tea is Nilgiri, greatly annoying Ciel.