Sonic (Roger Craig Smith) (now 16 years old) and his friends are ready to enjoy the rest of their lives peacefully. However, all of that changes when a new sinister Gem (Cherami Leigh) arrives, armed with a giant drill that saps the life force of all living things on Earth. In their biggest challenge ever, the Crystal Gems must work together to save all organic life on Earth within 48 hours.

Back at the castle, Eggman and Adrien are arguing. Adrien doesn't want to go to the ball since he wants to be a botanist rather than king, but Eggman tells him he is "going to be king and that's the end of it," after which Adrien leaves sadly for his waltz lessons. Right after, Orbot and Cubot appears and informs Eggman that Grandmother Fa agreed to the plan. Eggman then reveals he plans to kill Grandmother Fa after the king dies of poisoning so he would be hailed as a national hero. However, Eggman has one concern: his son, who is not very eligible, will need to find a wife. Cubot brings up Grandmother Fa's niece as an option, which raises Eggman's suspicions. Orbot mentions the niece as "purple with pink and indigo, about seventeen years old" and that it is an "interesting coincidence." Eggman asks Orbot and Cubot to bring the girl to him.

The castle is the domain of King Tom (Martial Minoux) and is where he was holding a concert in his name, performed by his seven daughters and the hedeghog court composer, Sonic (Roger Craig Smith). (''Daughters of Tom'') The concert goes as planned until it is discovered that Tom's youngest daughter, Marinette (Cristina Vee), is not there, much to his chagrin. (Everything did not go smoothly at the concert!)

Best friends, Marinette, Milo, Hiccup and Adrien use a special map that guides them through the Forbidden Forest, an enchanted wonderland that's filled with magical creatures. Their adventure leads them on a course to discover the biggest secret in Hero history as they race against time with the evil wizard, Hawk Moth, to find a mysterious village.