In Winterling, Fer (short for Gwynnefar, or Jennifer, as her father's mother calls her) saved a magical land from a wicked queen whose rule threatened to cast it into endless winter. Fer learned that her mother had once been the lady of this land, and that first book ended with Fer becoming lady herself.
Summerkin (HarperCollins, April, 2013), Fer returns to the land...but there are those who think that because she is human, she cannot be the true Lady. To prove that she is, Fer must compete in a challenge organized by the High Ones--and they aren't explaining the rules. All she knows is that if she looses, her Summerlands are once more in danger. Three will compete against her for the crown--a magical girl from a desert land, a Lich boy of the damplands, and a third from the High Ones realm, whose beautiful appearance belies a dark heart.
And in the meantime, Fer must figure out if she can truly trust Rook, the shape-shifting, surly, mischievous puck boy she thinks of as her best friend...and Rook must figure out if he can still be a wild, untamed puck and still be a friend to Fer. The story is told from their alternate perspectives, making this tension an integral part of the story.
The contest for the crown is no Hunger Games, and indeed these books are perfect for the kid whose still a few years too young for the violence of that series (ie, the fourth grader, give or take a year). Instead, Fer proves herself worthy not through physical prowess, or violence, but by being a good, caring, person. Which is not to say that it's not exciting, because it is.
The main interest for me, though, lay not in the action-full elements of the competition, but in Fer's struggle to figure out what sort of rular she wants to be, and her relationship with Rook. There's enough going on throughout the story to keep things from being bogged down in too much introspection, but enough of this character-centered element to the story to make it one I enjoyed lots.
If, like me, you want the boys in your life to read books with strong girl central characters, these are spot on--there are many mythological creatures and fantastical beings (a good hook for the young fantasy lover), set in a compelling, brisk story. My own boy (now 10) loved Prineas' Magic Thief books (me too), and so I should have no problem convincing him to try Winterling...
Here's another review of Summerkin at Random Musings of a Bibliophile.