This one actually does have a plot behind it, as I've moved it over from another request board I have.
There was once a book that held great powers. Within it's pages were that of another world completely. The Book of Fantasy was what the Ancients called it, and it had been lost for neigh on a millennia. It had been cleverly hidden within a Library, and one day someone literally stumbled upon it. Checking the book out from the Library MC just thought it was a normal fantasy book with a normal drab title.
Opening up the book, MC finds himself within a whole new world. He must find the Book again in this world in order to get home. Inside of the book, he gains powers inside from the realm. We can discuss if your character is inside of the realm, or happens to find the book inside of the Human world. That's as much as I've been able to think of, so we can brainstrom if you do this plot.