Those Vikings - Mike Cooper - Bog

Karl McGregor is twelve years old and friendless. He has a temper, so the other kids at school steer clear. Friendship's tedious until a new student, Adam 'Finch' Bird, enrols. Finch confides that his dad's in gaol; Karl says his dad is from the ninth century. Of course, Finch doesn't believe him. This is the 21st century after all. Then a mysterious object appears in Karl's shed. The boys investigate.
They stumble across a dubious history professor, who tells them they've found the gamban - a mystical Norse wand with incredible powers. In the ninth century, Norse God Odin lent it to the Vikings. The boys discover that Odin wants it back and is hot on its trail.
Against adult advice, the boys tinker with the gamban and activate its time travel function. They land at a farm in the ninth century, where they meet Erika. Finch gets a case of the jitters and demands they return to the 21st century. Vikings step in and capture everyone except Karl.
It's up to him to come up with a rescue plan.
Those Vikings is a tale of the fortunes and foibles of family and friendship. Set against the scary backdrop of a Viking invasion, it's aimed at readers 10-12 years old.