Hybrid - Shaun Hutson

Christopher Ward signed up with a literary agency on 12th December 1984 wanting to be SO rich it would be obscene. And he IS a success - but there is a price to pay. Nothing lasts forever...
As his writing ability begins to decline and publishers reject his books, he starts to drink. Sleeping badly, pacing around day and night, he gets a breakthrough. But is it? Pages of a novel pour out every night from the computer he's sure he's turned off and he doesn't remember doing the writing. He sets up a video to see what is going on - and sees ape-like shapes shuffling around. And the video shows HIM murdering a prostitute. What IS going on?
Then his literary agent comes round and shows that his life is the price he pays for previous success...