A planet was the place where a human colony ship crashed. The ship was fashioned into the Red Castle, and the colonists started a society that resembled a medieval kingdom. They enslaved the indigenous life forms, inhibiting them with inhibitor chips, and genetically altered them to be more like dragons, and also hunted them for sport. A man called the Dragon Lord freed them from being inhibited, and his "noble friends" murdered the royal family, but killed the Dragon Lord himself, while he tried to befriend the beasts and hunt the rest of the humans. A town set up a force field in the town to protect themselves. The Twelfth Doctor and Clara Oswald arrived in the Doctor's TARDIS, and the dragons snatched the TARDIS, taking it to their treasure horde in the Red Castle. After retrieving the TARDIS, the Doctor and Clara contacted the humans' homeworld for a rescue ship, warning that if the humans enslaved the dragons again he wouldn't come back to save them. The dragons were then left to roam their own world freely.