Torch by R.J. Anderson

Book 3 of The Flight and Flame Trilogy

Summary:

How do you fight fire without fire?
 
When a freak storm uncovers the entrance to a mysterious underground chamber, Ivy and Martin expect to find treasure. But what they discover is even more valuable: a barrow full of sleeping spriggans, magically preserved for centuries. With the vengeful piskey queen Betony determined to capture Ivy and her followers, the secret hideaway could be key to both their peoples’ survival.
 
But the piskeys and spriggans are ancient enemies, and when Ivy tries to make peace her own followers threaten to turn against her. Plagued by treachery, betrayal and desertion on every side, Ivy must find a way to unite the magical folk of Cornwall—or doom herself, Martin and everyone she loves to death at Betony's hand.
 
Yet without the legendary fire-wielding power that marks a true piskey queen, can Ivy convince her people to believe?

Opening Lines:

She'd only just found him again, and now he was gone.

Ivy sat on the front step of the house--not her house, a crude human cottage could never be home to a piskey-girl, but right now it was all she had--hugging her knees and staring gloomily into the night. The lights of a delivery van swept the front garden of the farmstead, turning toward the nearby village; on the hedge by the road a rook perched, watching her with a shrewd, glittering eye. Inside the house Mica still raged and stamped about, but Ivy was past caring what her brother did. The pain of losing Martin sat like a lump of cold slag in her chest.