The 1st half of this episode is the story Dream of a Thousand Cats. This is a beautifully animated tale about how the power of dreams can possibly re-shape your reality. It stays pretty true to the source material and any changes only enhances the story as one rebellious kitty tries to spark the dreams of her fellow feline friends in dreaming of a world where they rule over the humans.
The 2nd half is the twilight zone-esque tale of "Calliope". Back to live action, this story delves into the dark side of ambition and the desire to create brilliant work no matter the cost as a young writer enslaves and abuses the muse Calliope in order to end his writers block and fulfill his greatest desires of being a best selling writer. This story is important to the overarching narrative of The Sandman as Calliope was once the wife of the dream king himself Morpheus. The acting is top notch in this episode especially Arthur Darvill as the writer Richard Madoc who gives the despicable character enough humanity as to provide us with that dark mirror that reflects back onto us. The beautiful chemistry between Dream and Calliope was also a welcome development and provided emotionally compelling drama to the story.
This episode is a great example of some of Gaiman's best work on The Sandman being *close* to fully realized.