
Danny and Vlad’s game of revenge against each other begins with childish pranks, and, unfortunately for Danny, ends when Vlad decides to run for mayor of Amity Park! By overshadowing voters, Vlad wins in a landslide. The new mayor is eager to use his new power to make life as miserable as possible for Danny and his friends. He shuts down the Nasty Burger, outlaws technology, creates new school uniforms, and passes so many new laws in the name of “protecting the children” that Danny finds it impossible to go ghost.
The building boom in Amity Park upsets Undergrowth, the ghost of all things plant-like and vegetative. The green-thinking ghost takes over the town, turning everyone into plants themselves. All except Sam, that is, whom he makes his Earth-loving queen. Unfortunately, Undergrowth brainwashes Sam and uses her to attack Danny! Danny, meanwhile, has been battling a nasty case of the chills that leaves him too weak to fight. Escaping from Undergrowth in the Ghost Zone, Danny turns to his cold-loving friend, Frostbite,who explains that Danny is developing a new power. Now, Danny must learn to master his new freezing skill so that he can make his way back to Amity Park and pull the town out of Undergrowth’s leafy clutches.
After getting lost in the ghost zone, Danny and his friends find in a frozen zone the Infimap, a map that lets the holder to travel everywhere in the ghost zone. After Vlad Masters steals the map, Danny, Sam and Tucker must chase him through different times and places, from Salem to ancient Rome, to get this treasure before he manages to conquer Earth.