The dark half

Thad Beaumont would like to say he is innocent.
He'd like to say he has nothing to do with the series of monstrous murders that keep coming closer to his home.
He'd like to say he has nothing to do with the twisted imagination that produced his bestselling novels.
He'd like to say he has nothing to do with the voice on the phone uttering its obscene threats and demanding total surrender.
But how can Thad disown the ultimate embodiment of evil that goes by the name he gave it-and signs its crimes with Thad's bloody fingerprints?