Not the first in a series (but first isn't extremely high in cost).
Thorn Queen by Richelle Mead, is the second in the Dark Swan series, after
Storm Born ($4.79).
Book Description
Eugenie Markham is a shaman for hire, paid to bind and banish creatures from the Otherworld. But after her last battle, she’s also become queen of the Thorn Land. It’s hardly an envious life, not with her kingdom in tatters, her love life in chaos, and Eugenie eager to avoid the prophecy about her firstborn destroying mankind. And now young girls are disappearing from the Otherworld, and no one—except Eugenie—seems willing to find out why.
Eugenie has spilled plenty of fey blood in her time, but this enemy is shrewd, subtle, and nursing a very personal grudge. And the men in her life aren't making things any easier. Her boyfriend, Kiyo, is preoccupied with his pregnant ex, and sexy fey king Dorian always poses a dangerous distraction. With or without their help, Eugenie must venture deep into the Otherworld and trust in an unpredictable power she can barely control. Reluctant queen or not, Eugenie has sworn to do her duty—even if it means facing the darkest—and deadliest—side of her nature…