Experimenting with the Dragon Eye allows Fishlegs to find the location of Dark Deep, the ancestral home island of the Gronckles. Upon landing there, they find the island has been taken over by a massive new dragon called the Catastrophic Quaken. It's dangerous behavior forces the other Gronckles to leave and seek refuge on Dragons' Edge, much to everyone's dismay. Determined to win back Dark Deep for the Gronckles, Fishlegs allows Snotlout to train him in fighting dirty behind Hiccup's back in order to beat the Quaken and drive it off, but quickly find themselves outmatched once they confront it directly. They eventually learn the Quaken's behavior was out of loneliness and defensive instinct, and allow it to remain and share the island with the Gronckles.
