The great struggle for any artist — any great artist, anyway — is a philosophical skirmish in the context of a much larger war. Why should this story or song or drama exist? That’s the battle. Why does anything at all exist? That’s the war.

Unlike the brilliant 2006 movie upon which it is based, PAN’S LABYRINTH: The Labyrinth of the Faun (Katherine Tegen/HarperCollins, 256 pp., $19.99; ages 12 and up) screams both questions into the void. The film’s writer and director, Guillermo del Toro, and a co-writer, Cornelia Funke (author of the Inkheart trilogy), remain faithful to the script, but I don’t recall this fabulistic story of a princess trying to return to her kingdom during a brutal war being so unremittingly dark, despite all the bloodshed and grotesque violence that saturated the tale.

Set in fascist Spain in the darkest days of World War II, “Pan’s Labyrinth” stars 13-year-old Ofilia, a sensitive child who loves books, her mother, her dead father and her unborn half brother, in roughly that order. She and her mother have been brought to an abandoned mill deep in the woods by her sadistic, sociopathic stepfather, a captain in Franco’s army named Vidal, whom Ofilia calls the Wolf, at least until nearly the end, when Funke and del Toro apparently decide a spider is a more apt metaphor.

Vidal is obsessed with death, his own and others’. Pain and suffering are definitely his thing. He stabs out a boy’s eye with a broken bottle. He tortures a young rebel with a hammer and pliers. He executes resistance fighters and a kindly doctor who dared to help them, despite the doctor being the only hope in saving Vidal’s ailing wife and unborn son.

“Only fairy tales give evil a proper shape,” the authors observe early on, as if to justify the barbarity to follow. But you don’t need a fairy tale to fashion a character like Vidal. All you need is human history.

It doesn’t take long for Ofilia to learn from a magical creature called the Faun, the Pan of the title, that she is the incarnation of an immortal princess who escaped from the Underground Kingdom centuries before, doomed to wander the earth in different forms until she completes three tasks to find her way home.

A lover of fairy tales and books, Ofilia is given a magical tome by the Faun that will guide her to her destiny. She must rescue a golden key from an enormous toad that lives beneath a withered fig tree. She must brave the underground lair of the Pale Man, a skeletal, child-eating monster with eyeballs embedded in his palms.

The final task is a test that delivers a twist in the movie but here seems anticlimactic. In fact, Ofilia’s final, desperate act of selflessness jangles the aesthetic nerves. Hers is an obvious echo of Christ’s Passion, death and resurrection, but without the redemptive underpinning that made the whole thing worthwhile. Christ did not die to protect the innocent, after all, but to rescue the wicked.

Although the novel does not stray from the script when telling Ofilia’s story, there are sections interspersed among the chapters, styled as classic fables (“Once upon a time …”). These give origin stories to secondary characters — Ofilia’s father, for instance, who does not appear in the film. The stories are beautifully written, even charming and touching at times. But these dives behind the scenes of del Toro’s original creation seem dropped into the story haphazardly, bringing the plot to a screeching halt while we’re given information that has little bearing on the action.

And the tone of that action is foreboding and nearly unrelentingly grim. The novel takes the delightfully dark vision of the film’s writer-director (who seems to be an anti-fabulist fabulist, if there is such a thing) and approaches it all too literally. “There was no God,” Ofilia muses at one point. “There was no magic. There was only Death.” And then there’s this uplifting tidbit: “It was all lies. There was only one world and it was so dark.”

That about hits it right on the head.