[Lawtan]

After looking up the story and characters, I am highly doubtful that the Butler did it. Not because he isn't potentially meticulous and controlling enough to do so, but because he has made himself extremely vulnerable by not taking his heart medicine. Even if he was devoted enough to Lady Scrimshaw as to kill off a rival at the risk of his life, I doubt he would want her dishonor by having a guest die in her house. To my knowledge, he does not stand to inherit anything from dear departed Lord "I-have-too-long-a-name-so-of-course-I-am-dead". In short, there is no motive that does not have a more immediate and dire consequence to Alabaster...barring an accident.