An x-ray reveals a crayon lodged in Homer's brain. After the crayon is removed, Homer experiences a sudden surge in intelligence, making him closer to Lisa and isolated from his friends.
If you're not familiar with Terry Pratchett's Discworld series of books then you should first read this one before watching it. As always with book to screen adaptations the book is way better than the movie/tv show and as much of a cliche as that sounds it is almost always true. On the face of it though this was fantastic. To see your favorite Discworld characters brought to life on screen is worth the experience alone and although much of the book is left out it is still really gratifying to watch. Superb casting and brilliantly designed sets and effects make up for the omissions. I have no problem giving this 4 stars.