The Dark Half Hardcover – November 1, 1989 by Stephen King
 
From the Flap:

When Thad Beaumont wakes to the nightmare of George Stark, he hears birds, thousands of them, all cheeping and twittering at the same time, and with the sound comes a presentiment full of memory and foreboding: The sparrows are flying again.

Thad Beaumont is a writer, and for a dozen years he secretly published novels under the name of "George Stark" because he was no longer able to write under his own name. He even invented a slightly sinister author biography to satisfy the many fans of Stark's violent bestsellers. But Thad is a healthier and happier man now, the father of infant twins, and starting to write as himself again. He no longer needs George Stark, and in fact has a good reason to lay Stark to rest. So, with nationwide publicity, a bit of guilt, and a good deal of relief, the pseudonym is retired.

In the small town of Castle Rock, Maine, where Thad and Liz keep a summer home, Sheriff Alan Pangborn ponders the brutal roadside murder of a man named Homer Gamache. When Homer's pick-up truck is found, the bloody fingerprints of the perpetrator are all over it. They match Thad Beaumont's exactly. Armed with evidence, Pangborn pays the Beaumonts a visit, and suddenly he too is thrust into a dream so bizarre that neither criminal science nor his own sharp mind can make sense of it.

At the center of the nightmare is the devastating figure of George Stark, Thad Beaumont's dark half--impossibly alive and relentlessly on the loose--a killing machine that destroys everyone on the path that leads to the man who created him. As Stark approaches, as Thad and Liz contend with the escalating horror and implacable threat of his existence and Thad reaches deep inside his own mind to mount a defense, forces gather in the air above Castle Lake, outriders of the dead to the land of the living....To whom do they belong?

Here is The Dark Half, a tale of terror so real and fascinating that Stephen King's growing legion of fans will find themselves squirming in the master's heart-stopping, blood-curdling grip--and loving every minute of it.
 
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