On the rugged isle of Berk, a Viking boy named Hiccup defies centuries of tradition by befriending a dragon named Toothless. However, when an ancient threat emerges that endangers both species, Hiccup's friendship with Toothless becomes the key to forging a new future. Together, they must navigate the delicate path toward peace, soaring beyond the boundaries of their worlds and redefining what it means to be a hero and a leader.

It's been almost three decades since the rage virus escaped from a biological weapons laboratory. Still living in a ruthlessly enforced quarantine, some have found ways to exist amid the infected. One such group of survivors lives on a small island connected to the mainland by a single, heavily defended causeway. When one of them decides to venture into the dark heart of the mainland, he soon discovers a mutation that has spread to not only the infected, but other survivors as well.