Fishlegs discovers that Meatlug can produce "Gronckle Iron", a lightweight but extremely strong metal. Because their slow speed had previously allowed an Outcast boat to escape, Fishlegs decides that producing Gronckle Iron is a more helpful task than flying with the other teens, until Meatlug ends up ingesting a magnetic rock, attracting all the metal in the village-including Hiccup's metal leg.

When the town's well runs dry, Hiccup and Toothless discover the group of baby Whispering Death dragons in the tunnels underneath the village planted there by Alvin and the Outcasts, and discover a new dragon subspecies, the Screaming Death. The teens must drive the Screaming Death and the Whispering Death hatchlings away from the village before they destroy Berk.