The basic premise of Fables is that the characters from our fairy-tales are real people. They fled their homeland, pursued by a nameless enemy, and ended up in New York City, where like all immigrants they struggled to both assimilate and stay true to themselves.
The plot behind this particular collection is that someone has regained the power to rewrite the universe, and intends to scrap the world and start over. The Fables and the Literals team up to stop this from happening. But really, not much happens, and what does happen is cartoonish and silly. There are something like 5 pages of Bigby as a pink elephant. It's just...not good.