The Beast that Devoured the World
A monster has swallowed the sky and set fire to the seas. All the skies, and all the seas. Everywhere. In the entire world! Anybody who steps outside gets snatched up by a tentacle from the sky, and if you looked up carefully, you'd see them get chewed and eaten by that monster in the sky.
Somebody has to deal with it. Somebody like Toby, Leo, and Mariah . . . the sorcerers' apprentices.