After the understandable confusion a reader may suffer in Children of the Blood due to the timeskip and the slow return of memory, Lady of Mercy picks up right where book two left off. It’s in this third book that the structure begins to resemble a more standard Hero’s Journey, with a bit of the Prophecied Chosen One thrown in as well. Not that either of these were missing from the first two books, but it’s much easier to see when, well, most of the book consists of the characters traveling from point A to point B.
We still have Erin and Darin from the previous book, but now we add the mysterious Robert – a thief and skilled killer, and Trethar – an old mage whose power does not derive from blood. I may not have mentioned this before, but the power (magic, whatever) we’re accustomed to is that drawn from the Light and Dark Hearts. The Sundered – immortal servants of one or the other of the Hearts, born when the two first touched in the eons before time – have interbred with humans and produced the Lines. These halfbloods can wield the power of their parents, though its strength is much diluted in them, and it is only truly effective upon the enemy of those parents. So, the Bright Heart’s name is Lernan and the Lines of Light were Lernari, while the Dark Heart Malthan’s tools are the Malanthi.
The war between Light and Dark has ended at this point, with the fall of Culverne, last of the Lernari Lines, in the beginning of Children of the Blood. But that’s only five years before the start of Lady of Mercy, and the Empire’s hold is not yet unquestioned. For our heroes, it’s the start of their true battle.
Books one and two of The Sundered exist to set the stage. Into the Dark Lands explains the world and creates the history to while all else will refer. Children of the Blood becomes the immediate past which is still alive and well and influencing people. Now the real conflict can begin in Lady of Mercy. I suppose you can view this and Chains of Darkness, Chains of Light as two halves of a whole. The end of book three is the mid-season climax, or where Hollywood decided to end the first movie of the two they inexplicably decided to split a book into. Or you could make an argument for the first standing alone and the other three being something of a trilogy. Then again, it’s not as if the stories are totally separate, considering that there are consistent characters throughout and in the end there is a single Chosen One…ugh, this analysis is getting too complex.
Essentially, there is a great deal of rising action in Lady of Mercy and while it does have its own climax, it is a minor victory in the scheme of what remains to be accomplished.