Near the end of Fyodor Dostoevsky’s “Crime and Punishment,” the police investigator Porfiry Petrovich says to the student and murderer Raskolnikov: “I am a man with nothing to hope for, that’s all. A man perhaps of feeling and sympathy, maybe of some knowledge too, but my day is over.” Porfiry, affable and sagacious, believes in the ultimate benevolence of Raskolnikov’s soul, as well as the redemptive power of time served. He adroitly cajoles Raskolnikov to confess to the double-murder that has consumed his19th-century St. Petersburg and then, munificently, helps secure a reduced sentence of eight years of Siberian hard labor. Surely in the mind of British writer R.N. Morris, the statement above marks a rare misjudgment by the inimitable Porfiry, for in Mr. Morris’s new novel, “The Gentle Axe” (Penguin Press, 305 pages, $24.95), Porfiry receives another day. Mr. Morris has pushed the clock forward a year and a half; it is December 1866, and an ax-murderer has again struck “the city built on bones.” Never fear: Porfiry is on the case.

Mr. Morris, a freelance copywriter living in North London, who until now has published only short stories, has woven a smart, hypnotizing tale of crime and duplicity. Unlike “Crime and Punishment,” a deeply spiritual novel with sophisticated psychological underpinnings, whose challenge for the reader lies not in discovering the killer but in understanding him, “The Gentle Axe” is a standard whodunit, albeit a genuinely pleasurable one. Mr. Morris has tied a competent Gordian knot, replete with precipitous plot turns and “Da Vinci Code”-esque cryptograms. It is historically accurate, involving all levels of Russian social strata, from the aristocracy to the proletariat, and demanding that the reader juggle, along with deceptively critical details, a panoply of baptismal, patronymic, family, and diminutive names.

Porfiry in the original is a brilliant, compassionate detective who simultaneously condemns and justifies Raskolnikov’s actions. Ironically, in expanding Porfiry, Mr. Morris has rendered him less, not more, dimensional. This “fat little man” is a caricature of his former self, now a chain-smoking, infallible Jedi Master, who issues illogical, aphoristic proclamations. “Because I believe you have the potential for great good. But I fear poverty and hunger will lead you to acts that you regret,” he unjustifiably tells Pavel Pavelovich Virginsky, who, as a callow young man of self-imposed penury, serves as Raskolnikov’s doppelgänger.

In rationalizing whom he believes the murderer might be, Porfiry declares, “I feel it very strongly.” Dostoevsky’s Porfiry, though more organic, shares a propensity toward this wisdom of the viscera. It is not through the mere application of logic, both Porfirys contend, that one solves mysteries, but rather via a grasp of the suspect’s psyche — although even that may prove insufficient. In Mr. Morris’s most artful passage, his Porfiry explains:

I do not believe these mysteries are solved rationally, through the exercise of a cold, deductive reasoning. The thing that terrifies me — sometimes, when I allow myself to think about it — is that I don’ know how they are solved. One must go to a place within one’s self. It is a kind of Siberia of the soul. In the criminal, it is the place where these deeds are conceived and carried through. But we all have a similar place within us.

Mr. Morris ably describes the atmosphere of an oppressive and claustrophobic 19th-century Russia and its denizens. “Families lived side by side and almost on top of one another, every room divided and sublet to meet the rent. From one side of a curtain came the cries and cracks of a beating, from the other the frenzied thump of copulation. Everywhere in the back ground could be heard a gentle snagging sound, as regular and constant as the lapping of the sea an anonymous, muffled weeping.”

And no Dostoevsky redux would be complete without a young, sacrificial prostitute with a heart of gold. In “Crime and Punishment,” it is the devout Christian, Sonia who follows Raskolnikov to Siberia and, we are led to believe guides not only his spiritual atonement but also that of his fellow prisoners. Here, it is Lilya, Virgin sky’s lover, who, after her father excommunicates her, is forced in to the trade in order to support a bastard baby girl. She shares her tenement with a surrogate grandmother, who fills the apartment with “an abundance of icons.”

On every level, though, “The Gentle Axe” is an unambiguous detective novel. Mr. Morris may hope that his book is judged on its own merits, and in that light, it is a success. But having borrowed a beloved sleuth (Porfiry provided the inspiration for Columbo), he cannot complain when a reader readily longs for the profundity of the original. The difference rests not in intricacy of plot, but rather in seriousness of theme.

Any reader of crime fiction trusts that by novel’s end Theseus will be led out of the labyrinth. The fun lies not in the “if” but the “how.” When engaged with Mr. Morris’s story one never doubts, no matter how many red herrings, that Porfiry will ensnare his man. But what if we allowed our hero to fail? Would not the self-questioning that inevitably followed reveal more of his essence than any other full-length novel, regardless of how ingenuously executed? It is, after all, not Raskolnikov’s success in murder that defines him, but his failure to live with the secret.

Mr. Peed is on the editorial staff of the New Yorker.