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.

Hiccup convinces Stoick to ride a dragon to aid him in his duties as chief, but he quickly insists on riding Toothless on a regular basis, to both Toothless and Hiccup's dismay. Meanwhile, a mysterious dragon has been attacking the tribe's fishing ships.