The Moonstone is a mystery, so of course Wilkie Collins tried to make it as suspenseful as possible. One of the ways that he creates suspense is by allowing the narrators to drop hints about what is to come. The narrators aren't supposed to tell more than they knew at the time, but most of them can't resist the temptation. Gabriel Betteredge, for example, throws in the occasional hint about what will happen to Rosanna Spearman:
We will change the subject, if you please. I am sorry I drifted into writing about it; and not without reason, as you will see when we have gone on together a little longer. (18.104.22.168)
Almost all of the narratives are full of those little "as you will see" comments. Keep your eye out – which narrators seem to be able to keep themselves from dropping hints? What might that show about their characters?