The Dark Energy Chronicles

Erin has bonded with the dragon of Nevia, but until she can remove the elves' compulsion buttons from her arm she cannot become a true dragon-mother. Alec's skill along with the might of the dragon turned the tide in the first battle against the alien warriors, but the war rages on as they use their formidable weapons, dragon-knives, to counter the dragon. In a struggle to control the dragon, Erin remains compelled to help her former enemies fight the insurgents. On Earth, the Grand Cull has failed but the hydra monsters remain. Celeste must help her family on Nevia prevail in their war before she can return to Earth and face the growing threats from the elves there.