In an attempt to beat Dash in a haunted house decorating contest, Danny 'borrows' the enchanted sword of the Spirit of Halloween, the Fright Knight! When the evil, ghostly knight comes to retrieve his magic saber, he decides to stick around long enough to turn the real world into his own stormy realm of terror. Danny Phantom has other ideas, and banishes the Fright Knight to the Ghost Zone.

When Vlad Plasmius accidentally awakens the most powerful ghost of them all -- Pariah Dark, the King of all Ghosts -- Danny quickly finds himself the pawn in an action-packed, suspenseful game of chess. The only way to defeat the Ghost King seems to be a brand new Ecto-Skeleton battle suit that Jack and Maddie have constructed, but there's one big problem: wearing the suit can be fatal and only Danny can use it to defeat the Ghost King. With time running out, and the entire town of Amity Park sucked into the Ghost Zone, Danny Phantom must battle the all-powerful Ghost King to save his family, his friends, and even his enemies.

Danny and his friends get caught up in a time-traveling adventure. They are taken into a dark future, in which Amity Park is destroyed and the world's most powerful and evil ghost is Danny's own future self!