Where to begin?
The Eyre Affair is Jasper Fforde's first novel. It takes place in an alternate 1985, where literature is the opiate of the masses, and everyone is obsessed with Dickens, Keats and Milton. Airships take people skyward instead of planes and Richard III has been seen so many times by its fans that the theatres no longer employ actors, and instead just pick out random members of the audience to act out the story (with interesting Rocky Horror-style shoutbacks: "When is the winter of our discontent?").
The book follows the adventures of Literary Detective Thursday Next, working in Swindon's branch of the Special Operations Network's Literatecs (Special Operations 27, SpecOps-27 or SO-27 for short). The Literatecs' job is to deal with forged copies of Shakespeare and other writers, and it is through this that she is recruited to another section of the Special Operations Network to track down the theft of the original manuscript of Martin Chuzzlewit, one of England's most valuable treasures.
With no signs of entry and nobody showing up on the security cameras, the perpetrator of the crime must be Acheron Hades, who is so powerful that he can hear his name whispered from half a mile away. He has stolen Thursday's inventor uncle's most recent gadget: The Prose Portal. This allows anyone to enter any book, and talk to the characters and wander around the story, changing it as they go. The only drawback to this is that if it is used on the original manuscript of a book, all copies of it worldwide change in accordance to what you do (Nice and easy to avoid changing things in books with first-person narrative, but harder to do when there's a narrator).
Hades' plan? Hand over the money or Chuzzlewit himself gets a bullet in the face halfway down page 1, removing one of Dickens' best loved works from libraries everywhere, and it's up to Thursday to get in and stop him.
Throw in that the almighty multinational The Goliath Corporation want the Prose Portal for their own ends as well, and will do pretty much anything to get it, and you have an amazing book, with far too much going on for me to tell here, and I wouldn't want to ruin anything for people who haven't read it.
Thursday Next also appears in the sequels
Lost in a Good Book
The Well of Lost Plots and
Bless the GSD!
More information can be found at http://www.thursdaynext.com, including links to the SpecOps-27 site, Goliath's merchandising page, and fun things to do with your genetically reengineered pet dodo!