This question may not have a current answer but I want to be sure that I am not missing critical detail.
In chapter 129 of Kuroshitsuji on page 13 there is an eerie message etched into a wall that reads,
Who stole the candy from my tummy?
It is attached below with appropriate spoiler tags for anyone who hasn't read it yet.
Further in the chapter it is foreshadowed that Ciel has had some interaction with the persons who attacked the manor. However I do not recall who this is referencing or what arc.
Does anyone know? Or should I just wait for the future chapters?