Odin's Betrayal (Charlemagne's Cross, #1)

Francia AD853
After a failed Viking raid on the Frankish coast over 20-years-ago, Jarl Sven the Boar is forced to leave his only son, Torkel, as a hostage and warned never to raid Francia again or his son will die.
In Hügelburg, a small town in East Francia, Torkel and his 9-year-old son Charles are ambushed at home.
Before dying, Torkel thrusts a package into young Charles’s hands and tells him to flee Francia for Denmark in search of his grandfather Sven the Boar’s protection.
But the man Charles eventually finds is not who he expects, and Charles must put his fate in the hands of a man betrayed by Odin.
Together they must uncover the significance of the package and why the Kings of Francia want Charles dead.