Fifteen-year-old Tanner, with the good Beast Firepos the Flame Bird, is waiting to avenge his father's death by warlord Derthsin when Avantia is menaced by an evil army seeking the pieces of the Mask of Death, which allows its wearer to control all Beasts, and Tanner, aided by twins Gwen and Geffen, sets out to find the pieces first.

The war for Avantia has reached its terrifying conclusion! Tanner, Gwen, Castor, and Rufus have collected three pieces of the ancient mask that bestows the power to control all of Avantia's Beasts to the wearer. Only one final portion remains and it is being held in Derthsin's fiery volcanic lair.As the group travels toward the furious showdown, Tanner is plagued by the desire to put on the powerful Mask of Anoret. His struggle is amplified by the...

Tanner, his companions, and the Beasts continue their quest to retrieve the pieces of the Mask of Death, but Lord Derthsin's evil armies swarm over the land and his control over the people of Avantia continues to grow, until it seems that only the Beasts and their riders stand in his way.

As Tanner, Gwen, and their Beasts Firepos and Gulkien continue their search for the pieces of the Mask of Death, they face betrayal from Gwen's twin brother Geffen, and discover a new Beast-Rider pair--Castor and Nera.