The Size of the Moon by E.J. Michaels
Marcus used to ignore the things that went bump in the night. It cost him dearly. Now he helps Autumn track down these dark creatures, letting her do all the destroying...until the high-riser elves threaten his son.
Autumn is a warrior living in a time when warriors aren't needed, except to dispatch the occasional strig - a deadly creature that feeds off the living. Part elf and part human, she's been seemingly content for hundreds of years. Things change when she discovers she has deep affection for Marcus...a human. And now his life is threatened by the rogue elf that destroyed her family.
Vowing revenge, Autumn once again takes up the sword to hunt her old prey. Though the elves despise humans, they fear Autumn and unleash a fearsome hoard of predators to stop her. Yet the elves are about to discover how dangerous an enemy Marcus can be. He's prepared to go through man, beast and elf to keep from losing those he loves again...regardless of the consequences.