I can't fathom their motives, but I suspect they're somehow trying to turn the giants into weapons. The iron rune stonecallers and binders carry large tomes with them, which must contain the runes they're carving on the giants.
Capture the pieces of this book, assemble them, and bring it back to me, <name>.
Have you recovered the book?
<Prospector Belvar browses the book of runes.>
Hmm... there's so much here. I'm going to need some time to study it, and if we hope to understand these runes, we'll need to try to make our own.
Kill Stonecallers and Binders. Collect the three chapters and combine them. Keep an eye out for the pathing 70 elites!