Snotlout becomes convinced he is dying having seen "The five signs of Valhalla", claiming that after seeing a singing tree, falling chickens, and sheep chasing him, etc, that he would die, and wants young Gustav to be his replacement including taking care of Hookfang in case he died. But when Snotlout "miraculously" recovers (the five signs he saw were really pranks played by Ruffnut and Tuffnut), he takes his dragon back, and Gustav decides to get a dragon of his own (named Fanghook) and join the academy… whether they want him to or not, especially as the Dragon Riders plan to stop Dagur the Deranged's new plan.

After rescuing Trader Johann, Hiccup and Toothless return from a mission to find Berk mysteriously empty. They discover that the village has been overrun by Speed Stingers, a non-flying dragon that move at blindingly fast speeds and can paralyze their victims with their tails. The Speed Stingers have trekked across the frozen sea to Berk and driven everyone out of town. Now, Hiccup must find a way to drive the Speed Stinger horde away from Berk before their next raid.