Seven Days To Save The World And Other Homework Projects

One day when bullied Florian comes home from school, he finds a visitor in the caravan where he lives with his father.
The woman, who looks older than time, tells him that his father is king of Celestia and has seven days to renew the spell of protection over the land.
But his father has no interest in going back.
So Florian finds himself with a crown on his head, having to complete a task he has no idea how to do, on the way across the sea-bridge to Celestia.
He has some companions: his father three motorcycle-riding friends who insist they're elves, and his father's horse, which is a unicorn in disguise.
The problem is that the elves haven't been to Celestia for a long time either, and the horse has always hated Florian.
An extra problem is that the unofficial queen of Celestia, Florian's mother, doesn't want him back. She is under the control of powerful magical spirits.
Did I say Florian knows nothing about Celestia or about magic? And he has only seven days?