Undraland by Mary Twomey

After her parents and twin brother died a year ago, Lucy Kincaid was determined to put together a normal life for herself. With her heart set on college life, Lucy’s dreams of medical school are dashed when a rabid bear attacks her in the middle of suburbia.

When Jens, a handsome yet irritable stranger, saves her life, Lucy’s gratitude is cut short when he abducts her, taking her to Undraland, a land filled with people and creatures she remembers from bedtime stories she assumed were just Scandinavian folklore.
Jens takes Lucy to a world she never expected, and cannot escape. Undraland is teeming with oversized garden gnomes, warrior elves, Nøkken, Fossegrimens, and worst of all, Sirens. Lucy goes further and further down the rabbit hole until she signs up to join a band of thieves bent on taking down Pesta, the last Siren.