Having just arrived above the surface after defeating Makuta, the Toa are surprised to find the opposite of peace. They learn from a fleeing Ta-Matoran that the Bohrok have attacked. The Toa race to Ta-Koro, to find the Bohrok storming the village. They fight them off, capturing one. TuragaVakama explains the legend of the Bohrok, the secret of the Krana, and what they must do next. The Toa return to each of their villages to capture Krana, with even Gali reluctantly agreeing that in this case they should split up. Pahrak attack Po-Koro, then Lehvak join them as well. Pohatu manages to collect a few Krana during this onslaught. Onu-Koro is attacked by Nuhvok, but Onua finds their autocratic nature to his advantage as he easily tricks them into submission. As Lewa reaches Le-Koro, he discovers it has been taken over by the Bohrok; all the Matoran of the village, and Turaga Matau, are under the control of Krana. The Le-Matoran jump on Lewa, who dares not fight his own villagers. A Krana is placed on his face. Kopaka, having followed several Bohrok Va to an isolated spot which turns out to be the entrance to the nest, shows Tahu his discoveries. He wishes to plunge in but is warned against it. Through trial and tribulation the Toa are united, Lewa having been freed with the help of Onua convincing him only he has power over his own mind. Tahu, learning this, doubts Lewa's intentions as a Toa but they all still work together to a solution.The Toa decide to go into the nest. Lewa realizes that Makuta released the Bohrok through his weak link to the swarm. The Toa soon encounter a strange impenetrable wall. Tahu explores an opening, but gets trapped in the Bohrok nest below. Kopaka soon realizes that a lava flow is heading towards the Toa. He temporarily stops the lava with ice, but does not expect it to last long. They all try with all their might to break open the wall until Lewa realizes that the strange wall is actually an illusion. The Toa pass through the wall but have little time to relax as Tahu blasts the Bohrok nest apart by heating the air up, breaking into the room the other Toa were in, causing them all to fall into a lower chamber. The Toa find niches into which their collected Krana fit. The Krana unlock six passages to the Exo-Toa, which the Toa don. As they put on the powerful suits of armor the Toa face the Bahrag. They use the Exo-Toa's power to drive the Bahrag to the center of their chamber, but this only increases the Bahrag's power. Realizing the Exo-Toa hinder Elemental Power, the Toa shed them, and blast the Bahrag with a single beam of all six elemental powers combined. The Bahrag are trapped in a cage of solid Protodermis by this, an unexpected result to both them and the Toa. Before their shock can register the ground beneath the Toa sinks, plunging them into Energized Protodermis. They are transformed into the Toa Nuva, and with their new powers, they escape the collapsing roof.