Cast Out (Part 1)

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.