Bionicle: Challenge of the Rahkshi (Bionicle #2)

The Toa Nuva suffer a mysterious loss of their powers which threatens their very existence. It's the work of the Bohrok-Kal, a special squad of mutated Bohrok who seek to free the swarm queens and unleash the Bohrok again. With the help of the legendary Mask of Time, the Toa Nuva are able to defeat the Kal.

Meanwhile, a Matoran village named Takua has stumbled upon the long-hidden Mask of Light. He and his best friend, Jaller, are sent by the village elders, the Turaga, to find the Toa to whom the mask is destined to belong. But Makuta unleashes twisted creatures called Rahkshi against the island in an effort to stop the Toa of Light from coming into being. After many defeats, the Toa Nuva unite to stop the Rahkshi with the help of Takua, who dons the Mask of Light to become Takanuva, Toa of Light. Takanuva challenges Makuta in battle, a fight which leads to the discovery of a huge underground island city – Metru Nui.