Long ago, the Pop Music Trolls were divided into two separate tribes on opposite sides of the river. For two centuries, the Trolls of the north lived happily and in harmony, even making friends with Trolls who liked different types of music. The Trolls of the south, on the other hand, grew bitter, distrustful and lonely. Now, both sides each face their own problem and the only solution is to reunite as one, but neither side fully trusts this idea. Eventually, Queen Cyan agrees to join her kingdom with King Peppy's... Under the condition that his daughter marries her son.