In the previous chapter, Sebastian is found dead presumably murdered by the same murderer who killed Lord Siemens (back in Chapter 40). Before he supposedly died, he has set up some instructions for the Phantomhive household servants.
In chapter 42, Sebastian is said to have been stabbed and hit on the head and from there, the master writer speculates that he may have been killed by multiple assailants. In the wake of Sebastian’s “death”, Ciel had the butler Tanaka-san replaced the “deceased” as his main butler and oddly enough, Tanaka-san appeared to be normal as opposed to the tea-sipping chibi version of him that we usually see. I guess that when the situation requires it, Tanaka will be back to his normal self.
Although the murderer(s) is still at large, the day resumed as per normal. Dinner is served promptly and all guests are present at the dining table except for one. And so, in the pouring, thundering rain, a third murder is committed when the body of the missing guest is found.
In the final scene of this chapter, the owl that Sebastian entrusted to Mei Lin flew out with a letter strapped on its leg as instructed. I wonder, what is the contents of the letter and to whom the letter was addressed to…
Me thinks that the part where Sebastian is supposedly dead by murder is staged by both himself and Ciel to lure out the murderer. Either way, I doubt that Sebastian will die easily seeing as he is a demon and all.
Note: This post is written based on Kuroshitsuji chapter 42 scanlated by Bleach Asylum.