When Magic Fails — Alaina Stanford

After Sarah exerts too much magic battling the changeling, her friends have no choice but to trust the trolls. These same trolls who took Todd Hopper off in the darkness less than a year ago under the same pretext and he never returned. Cabal, Jack and Nicole allow the trolls to lead them deep inside the mountain so Sarah can recover in the safety of the caverns.

What they find there shakes them to their very core and changes Sarah's life forever as they are forced to head into a battle that pits friend against friend.