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!