It's a world very like ours, only different: the Crimean War is being fought (in the 1980s), dodos and mammoths still exist, time can be altered, and changing a manuscript changes all copies of the book. This is the world of Jasper Fforde's Thursday Next, an eccentric alternate world that operates entirely on its own hilarious rules.
The Eyre Affair introduces Thursday, who works for Jurisfiction, a special division dedicated to protecting literature. She is currently on the trail of the malevolent Acheron Hades. First Hades kills a minor character from "Martin Chuzzlewit," and then kidnaps Jane Eyre (in this parallel universe, the novel has a very different ending). Thursday Next teams up with the brooding Rochester and an odd bunch of characters to save Jane—and all the other great works of literature.
Fforde peppers his books with countless delightful literary references (Lewis Carroll, Falstaff, the Questing Beast, Mr. Toad), and he gives them a wink-nudge twist worthy of the best of British comedy (this is a world where great art is pop culture). He can also wrench your emotions with rare delicacy.
And Thursday is a delightful heroine—she's one of a very few heroines who starts off hardened and jaded, but becomes more vulnerable as the series progresses. We get to see her go through some pretty weird adventures, dealing with them in her slightly dry, very capable style.