Fragile Destiny by Suzanne Lazear

Noli and her true love V fear the worst if the Staff of Eris—a potent Otherworld relic—falls into the wrong hands. Broken into pieces and hidden in the mortal realm long ago, the staff bestows vast powers on whoever possesses it. Ciarán, the dark king, is trying to rebuild the staff, intending to use it to install a new queen.

In a desperate effort to keep the Otherworld from falling into darkness, Noli and V plot the daring theft of a jewel Ciarán needs to complete the staff. But Ciarán is not so easily defeated. Through his devious machinations, he has set a plan in motion for a final showdown that will decide who rules the Otherworld once and for all.