A
dark fantasy novel by William Browning Spencer. Harry Gainesborough, a
children's
book writer, falls in with a group of escapees from a
psychiatric hospital where he once spent time while recovering from the
death of his
daughter, and in which he wrote his most popular book
Zod Wallop.
The fugitives behave as if the story in Zod Wallop is true--that they are the good characters in the book and the various authority figures who are after them are the evil characters. A series of wildly improbable events (such as a monster from the book swooping down and attacking Gainesborough's car) convince him that there may be something to this, and that it all centers on a secret experiment they were all subjected to.
Imagine a combination of the Harry Potter and Gormenghast series with the "alternate realities or mental illness?" themes of Philip K. Dick and you'll get an idea of the feel of this book. A good read, though I found the ending a bit too pat.