One night, Rainbow Dash has a nightmare about a human boy, calling himself Death, bringing ruin upon Equestria. She wakes up the next day to find that this boy is real, and that he has mysteriously arrived in Equestria from another world entirely. Soon after he arrives, he comes into contact with a fragment of a magic mirror, and connects two worlds long thought to be forever separated. Amidst the chaos that ensues, dark beings from the boy's world, being who had been presumed dead, resurface, seeking to use the chaos to their advantage...to destroy both worlds forever.