From an Interview
with Sarah Prineas on the blog "The Enchanted Inkpott"
There are two big plot/character arcs in SUMMERKIN. One is that Fer has to prove herself as the true Lady of her land, which involves some rigorous testing and some revolutionary moves on her part. The other big arc is that of Fer and Rook's friendship. Rook is a much bigger character in this book--more of a co-protagonist--and he's pulled one way by his loyalty to his brother-pucks, and the other by his ties to Fer. His capacity for true friendship is really tested.
Fer also makes some new friends. One of them is named Gnar and is a fire-girl who rides a dragon and is ridiculously fun to write.