"Horns" could not have been an easy nut to crack. Based on the supernaturally wild 2010 novel by Joe Hill, this big-screen adaptation from director Alexandre Aja (2010's "Piranha") and screenwriter Keith Bunin (HBO's "In Treatment") very readily could have become an over-the-top, unintentionally foolish blunder, the kind where an enthralling, fantastical literary work gets lost in translation once performed in front of cameras. There is better news to report with the finished outcome of "Horns," which, above all, persuades the viewer into believing its increasingly convoluted plot. Though streamlined from the source material, the picture might have benefited from a further stripping-down during the bombastic, CG effects-laden third act. Fortunately, the essence of the love story at the center of a lot of literal fire and brimstone remains.

Since the unsolved murder of girlfriend Merrin Williams (Juno Temple), Ig Perrish (Daniel Radcliffe) has become a pariah in his Seattle hometown. Merrin's father (David Morse) believes he killed her, and even his own supportive parents (James Remar and Kathleen Quinlan) shield underlying doubts about his innocence. When Ig wakes up one morning with horns inexplicably protruding out of his head, a trip to his doctor leads to a revelation: everyone with whom he comes into contact experiences the uncontrollable urge to speak the truth. Using this newfound power to his advantage, he sets out to investigate the events that led to Merrin's death, eventually joining forces with an army of snakes to help do his bidding.

"Horns" is an eccentric genre hopper, a hybrid of horror, fantasy, mystery and romance that threatens to overstuff itself by the last half-hour. The special effects that bring Ig Parrish's reptilian menagerie to life sporadically look believable and other times do not at all, tarnishing the tricky balancing act of a premise that is already kind of silly. Certain side characters, like Ig's parents and Glenna (Kelli Garner), a childhood friend whom he sleeps with, are underused, victims of a final cut that already runs long at two solid hours. Where director Aja goes right is in his treatment of the soul-infused love shared between Ig and Merrin. Daniel Radcliffe (2012's "The Woman in Black") is terrific in the lead role, giving just the right amount of edginess to Ig that leaves one questioning whether he has it in him to be a sinner or a saint. And Juno Temple (2014's "Sin City: A Dame to Kill For"), as the ill-fated Merrin, touchingly essays a young woman whose reasons for breaking up with Ig the same night she died run far deeper than he can imagine. "Horns" has trouble reaching a conclusion that is wholly satisfying, and yet much of what comes before it works on a surprisingly identifiable emotional level. Take out Ig's horns and snake attacks and special powers, and what is left is an attentive exploration of fate and loss that flirts with profundity.