Melvin Burgess 
Bloodsong [EPUB ebook] 

PART II Fifteen-year-old Sigurd, son of King Sigmund, is the last surviving member of the Volson clan. His father’s kingdom — the former city of London — is gone. And his father’s knife, a gift from Odin himself, has been shattered to dust. Now, Odin’s eye is upon him. Armed with a powerful sword forged from the remnants of his father’s knife, Sigurd will face death, fire, and torment. He must travel through Hel and back…to unite his country once again.