The dragons unintentionally cripple Berk's food productivity by terrifying the local livestock, and with the year's first winter storm coming, the dragon-riding Viking youths of Berk must try and familiarize the local animals with their dragon companions if they are to have enough food for the winter.

The dragons are blamed for vandalism, and Hiccup tries to prove their innocence by forming a night patrol called the "Dragon United Monitoring Brigade" (DUMB), but not in time to prevent the dragons' banishment from the island. Hiccup begins to suspect that Mildew is responsible for the damage.