The war against the Insectors continues in the Inner World, a hidden realm beneath the Earth. Hunter Steele and the Spider Riders stand guard over Arachna, joined by Igneous, a sharp young royal officer, the reckless fighter Magma, and the gentle Corona. When word arrives that the Insectors have struck the Kingdom of Nuuma, the Riders hesitate to leave Arachna exposed. They owe Nuuma a debt, though, so they cross the Inner Ocean to help. Hunter's task is to recover the four keys belonging to the Oracle, which Mantid, ruler of the Insectors, has locked away. Mantid wants to take the Inner World for himself. This second and final season of Spider Riders is an action adventure with mecha elements.