I'd also like to nominate A Suspension of Mercy
by Patricia Highsmith.
Sydney Bartleby has killed his wife, Alicia—at least he has thought about it, compulsively, over and over again, plotting schemes, designing escapes, forging alibis. Of course he has; he's a mystery-script writer. But when Alicia takes a long, unannounced vacation, Sydney seizes the opportunity to perfect his artistic method.
With her characteristic precision and unrivaled sensitivity to the inner tremblings of human character, Patricia Highsmith shockingly portrays Sydney's descent into the treacherous world of his own fictions. Once again Highsmith proves herself to be a master at depicting the unsettling forces that boil beneath the surface of everyday life
Available all over and couponable (Kobo has several active coupons right now, and Sony has a coupon this weekend).