Weapons of the Wolfhound by Moyra Caldecott

It is the 12th century AD. Neil lives with his parents on a farm on the remote island of Lewis in the Outer Hebrides. Bored with his days and longing for excitement, Neil travels with the Viking warrior Baldur to Iceland to visit Baldur's father, the Wolfhound. But Baldur's father has died, and his grave has been robbed of the hero's famous weapons. Baldur's anger is intense, and he and Neil go on a dangerous journey across Iceland to recover the stolen weapons -- the Weapons of the Wolfhound.