Dagur the Deranged visits Berk to renew a peace treaty between the Hooligan Tribe of Berk and the Berserkers, and the dragons are put into hiding to dispel rumours that Berk is training a dragon army, which will make Dagur cancel the treaty. But when Ruffnut and Tuffnut begin to fight, their dragon, Barf and Belch, is left out of control. The Viking teenagers must bring the twins back together to control their dragon and avoid provoking Dagur to war.