Those who consume their mysteries with earnest seriousness are ill-advised to tackle The Fourth Bear, which kicks off with the death of Goldilocks, a cucumber explosion and an investigation of bears doping up on porridge. It's hard to derive the standard reading pleasures when a crime novel's prime suspect is the Gingerbread Man. Jasper Fforde's follow-up to The Big Over Easy continues to track the sleuthing of Jack Spratt (of "Spratt could eat no fat" and beanstalk notoriety), a nursery crimes investigator who, like all dependable literary detectives, is at odds with his colleagues and is thoroughly mucking up his personal life. Not only is Spratt chasing down the most malevolent psychopath his town has known, but he also has been taken off the case for botching a previous investigation. It's a conventional detective novel set-up — which is good, because toying with convention supplies Fforde with his best material. This killer, after all, has a "licorice mouth curled into a cruel smile." Jack, assisted by Detective Sergeant Mary Mary, is a protagonist for our irony-laden times, always aware that he is within a novel. He dryly resolves to pursue the Gingerbread Man "against orders, catch him, cover ourselves with glory, and (make) the by-the-book officers look like idiots." Fforde's fans will gleefully follow the inevitable fulfillment of this prophecy, a romp complete with madcap chases, flying chunks of diabolical gingerbread and, finally, an answer to the age-old question of how three bowls of porridge poured at the same time got to be different temperatures. Humor depends on an element of surprise. By playing so fast and loose with fairy tales, Fforde (who also writes the Thursday Next series) licenses himself to turn his sentences in unexpected directions, which results in a compendium of giddy delights.