Of Starlight and Midnight by Amy Kuivalainen

Of Starlight and Midnight combines adventure, romance, magic, and Norse myth and shows that some Fates are worth fighting for, especially when the Norns get involved.
It's been two years since light-elf brothers Aramis and Søren fought beside Anya in Russia. The Álfr mountain city of Svetilo is safe once more, but their books and relics are still scattered on the supernatural black market. When Aramis gets a lead on a book of magic, he and Søren decide to investigate and find more than they bargained for.
Librarian Asta is still grieving over the death of her mother. All she wants to do is hide at the University of Oslo, unravel the mysteries of the strange book she inherited, and hang out with Tyra-the cool Norwegian cousin she never knew she had. The last thing she wants is to help arrogant Dr. Søren Madsen work on his book, no matter how good-looking he is, but she doesn't want to get fired so she reluctantly agrees.
Søren knows Asta is hiding something and when they are attacked by dark elves, he and Aramis will stop at nothing to learn the truth about the two mysterious women. But Tyra has a past of her own, and she'll do anything to protect Asta's secrets, even if it means siding with the dangerous light-elf brothers in a deadly war of dark and light.