Both worlds, demigods and magic must join together to defeat their foes. But they have been rivals for a long time, unable to agree on anything aside that they hate each other.
Percy and his friends received a message from the gods, telling them to reunite the two worlds and bring peace once again. He dreams of a castle, people roaming around wearing dark robes and carrying strange sticks. He gets an invitation to Hogwarts and along the way, he will meet new friends, face new foes, and make new experiences.
Harry is having dreams, some nightmares. In his dreams, he sees a boy, his eyes see green, his hair black and messy, together with two more people, they wander around, a sword in his hand. When he tells this to Dumbledore, he reckons they should work together to defeat the dark lord. He will be surprised by the events, things he never thought would have happened.
Will they be able to team up and fight? Or will the two worlds be forever split apart, and destroyed, one at a time, little by little.