Phoebe Howell and her unicorn best friend, Marigold Heavenly Nostrils, are headed to music camp for the summer, where they form a punk rock group with fellow campers Sue and Stevie. Marigold also discovers a portal to a parallel dimension where she and Phoebe come face-to-face with the dark and sinister versions of themselves. Throughout their magical and musical adventures, the best friends learn about the value of friendship.