When Trader Johann delivers mass quantities of metal to Berk that came from Breakneck Bog, the island becomes infested with Smothering Smokebreaths, that steal the town's metal to build a new nest. With no metal, and especially no weapons to protect their village, Hiccup and the others must find a way to get rid of the rogue dragons, only to discover that the Smokebreaths' appearance was planned as an attack by Dagur the Deranged.

After Snotlout accidentally puts Astrid in a near-death situation, Hiccup suspends him from the academy for disobeying the rules one time too many. However after he and Hookfang are ambushed by the Screaming Death on Snotlout's secret island, "Snotland"', he is rescued by Alvin the Treacherous, who has returned to Berk, claiming he is there to make amends with the Vikings. Despite the fact that nobody trusts him, Alvin's warnings allow them to defeat Dagur's invasion, but before they can destroy Dagur he captures Stoick; Dagur flees back to Outcast Island with his captive, demanding Hiccup and Toothless in exchange for Stoick's life.