The Viking boy Ubbe Gunnhildsson is on the hunt for the terrible Fenriswolf that killed his mother. Along for the ride is his friend Thyra, the crazy Harald Bluetooth and the god Loki in raven form.
An equally important mission is to get hold of the goddess Idunn's apples. They can heal Ubbe's brother, who was blinded during the Fenriswolf's attack.
Suddenly, their journey towards Åsgard is stopped by the Thunder God himself. During the showdown against him, a shocking revelation occurs: the Fenriswolf has been in their midst the whole time.