On the one hand, Arsène Lupin only happens towards the end of the novel, and the story does not absolutely turns around.
Moreover, the plot is not in the usual style of AL. Here, the story lacks some dynamism, but it is better to give it structure. We find ourselves so immersed in the world of thirty coffins in the mood.
Or at least it tries. The quick little style that we fall asleep easily, and as the emphasis is not placed on the suspense, it is easy to get discouraged. It would be a mistake, since it is precisely the end that is the best part of the book.
But it is true that this may be a work reserved for those who have already made the round-up of other novels of Maurice Leblanc.