Dean Koontz: Shadowfires [1991] paperback

Rachael Leben's violently possessive ex-husband, Eric, hideously mangled in a freak accident, is dead. But his body has disappeared from the city morgue.

Now someone, or something, is watching Rachael. Calling her. Stalking her. And though no one will believe her, she knows who it is; that his walking corpse is a grotesque mockery of life, and his brilliant, warped mind, once again 'alive', is seething with jealous rage, seeking an unspeakable revenge.