Three young Thunderdrum dragons have arrived in Berk. Hiccup tries to train them so they can stay on Dragon Island, but the dragons are mischievous and just won’t behave. They’re causing too much trouble! Hiccup realizes he may have to send them away — but they won’t be safe on their own. So he and his friends have to come up with a plan to protect them and help them learn to behave well.