Just when the evil Dr. Blakk has been defeated and it seems like Eli Shane’s duties as protector of Slugterra are getting easier, a new danger emerges from beyond the 99 caverns. Eli and the Shane Gang rush to the rescue, but nothing can prepare them for what they encounter: a slug that can do something no one in Slugterra has ever seen — or heard — a slug do before! Traditional slugslinging no longer applies — Eli will have to engage in a very different kind of duel to save Slugterra...and himself!

A new member has joined Eli and the Shane Gang! Junjie, once the protector of the Eastern Caverns, is a master of the slugslinging art of Slug Fu! But even with the power of five slingers, the Shane Gang find themselves in over their heads as they race across the 99 caverns in search of the legendary Elemental Slugs. The five Elementals are ancient slugs of great power, and the forebearers of all slugs found in Slugterra today. In the wrong hands, they could bring Slugterra to the brink of destruction. So, when an evil alliance starts hunting down the Elementals, Eli and his friends — both old and new — take off in pursuit of the greatest threat their world has ever faced!

Eli has added some awesome new slugs to his arsenal: the extremely powerful Elemental Slugs. But in order to control them, Eli must learn Slug Fu--the ancient form of slugslinging that Junjie mastered in the Eastern Caverns. Slug Fu is the art of guiding and controlling a slug in battle--a skill that only the greatest slugslingers can master.