In any classic story, there's certain plot points to hit for it to be said classic. If you're talking Romeo & Juliet, you need Romeo to be told that Juliet's dead. In Jane Eyre, it's Mr. Rochester's first wife getting out and burning the house to the ground. Or, in Harry Potter, it's that whole Voldemort choose to attack baby Harry over baby Neville. What would happen if these details changed?
Write a story in which a certain plot point from your favorite book was altered.
The goal here is to inspired by the original piece, but also to show your creativity. Whether you change something large or small, it should show the theory of unintended consequences. Let each change, starting with the first, be a series of dominos that finishes by dramatically changing the story's end.
If you can alter the story's themes while you do so, even better.