Tom has to keep his mom, Olivia, distracted while Jun, Alex, and D'Angelo use a new dragon to close off a cave leading to the Crystal Realm, and prevent her from discovering the dragons.
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 up 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 a group of misfit kids, brought to the site by their parents, uncover the truth about dragons and where they've been hiding - a secret they must keep to themselves to protect what they've discovered.
Dragons: The Nine Realms - Dragons of the Undead Synopsis and Schedule