Black Butler, Vol. 7 (黒執事 [Kuroshitsuji] #7)

Having successfully infiltrated the Noah's Ark Circus in the guise of
rookie performers, Earl Ciel Phantomhive and his butler, Sebastian, set
about gathering clues backstage as to the whereabouts of the missing
children. But when a turn at a snooping puts Ciel on the trail of a man
whose identity is shrouded in mystery, he sets his consummate manservant
to the task of investigating further. This time, however, Sebastian
must call upon one of the more infamously wicked skills of his kind to
solve the puzzle. As he stalks his vulnerable prey in the shadows of the
fairgrounds, is his young master prepared for where the ill-gotten
gains of his butler's methods will lead?