Witching Season by Yasmine Galenorn

Raven and Kipa return to Seattle when a new threat appears. A cult, bent on reviving an ancient elemental goddess, begins to unleash havoc on the city with a string of odd murders, endangering anyone traveling on or near the waterfront. During their investigation, Raven and Kipa discover the danger is far greater than they anticipated. And now, a previously forgotten race of Fae is emerging, threatening to upset the balance of the Light and Dark Courts.