As for plot I just know that since Ciel was going to investigate it more that means Sebastian is part of it as well. Armin was going to go missing for a bit with his journal lost too so no communication with him, and then Ragna was going to be in denial about everything because this type of plot is pretty much one of his worst nightmares so he was going to be in a bubble of "nope".
That's all I had signed up for so far and I believe that's the order of it.