Set 1,300 years after the events of “How to Train Your Dragon,” dragons are now just a legend to the modern world. When a geological anomaly opens an immense, miles-deep fissure in the Earth’s surface, scientists from all over the world gather at a new research facility to study the mysterious phenomenon. Soon after, a group of misfit kids uncovers the truth about where dragons have been hiding — a secret they must keep to protect what they’ve discovered.