What important twist occurs in Chapter 87 and how does the author use it to build suspense?

Chapter 87 ends with Sophie and Langdon losing the keystone, which heightens the suspense greatly, because it is now in the hands of two violent men who have taken their friend, Teabing, as a hostage. The author, Dan Brown, uses this section to toss yet another twist into the story. Since the keystone is now in the hands of the wrong people, we're left wondering what will happen next.