Another heaping helping of middlebrow mush from Nicholas Sparks, the modern-day version of Fannie Hurst, “The Lucky One” is even sillier than previous adaptations of his morbid, inexplicably popular books. And it’s yet another indication that in trying to shake the teen-idol image of the “High School Musical” series, Zac Efron is making some very poor career choices.

Efron is Logan Thibault, the hero of the picture, an Iraq war vet and suffering saint who survived three tours by clinging to a photo of an unknown woman that he found on the ground after a firefight and, now that he’s returned from combat, determines to thank her for saving his life. Accompanied by his faithful dog, he literally walks from Colorado to Louisiana, where he finds Beth (Taylor Schilling), a lovely divorcee with a darling young son named Ben (Riley Thomas Steward). She lives with her feisty grandmother Ellie (Blythe Danner) and together they operate a rustic dog kennel.

But unable to disclose why he’s come to Beth—still distraught over the death of her brother, also a Marine, in Iraq—Logan instead takes a menial job at the kennel, and with his soulful but ingratiating air quickly enchants both Ellie and Ben. He also gradually wears down Beth’s hostility, much to the displeasure of her ex Keith (Jay H. Ferguson), a redneck cop with a powerful pappy (the local judge) and a mean, possessive streak.

All that “The Lucky One” really does is provide a platform to demonstrate Logan’s perfection, despite (or perhaps because of) the hardships he’s endured. He helps Beth overcome her debilitating pain over the loss of her brother (the siblings were so close because they lost their parents in the inevitable car crash “when they were young”). And he brings Ben out of his shell, playing chess with the boy and enticing the shy lad to play the violin in public at church (Logan accompanies him on the piano, yet another of his inexhaustible array of skills, which also include taming any recalcitrant pooch and fixing any broken machine in sight, whether it be an old tractor or the family’s derelict fishing boat).

There’s one person Logan can’t win over, of course—Keith, certainly the worst written role in a script in which everyone is a cliché (laconic stranger, grieving sister, sitcom-precocious kid, all-wise grandma). Until the last reel Keith’s just a nasty jerk, but toward the close he turns drunkenly belligerent, then regretful, then angry again, and then self-sacrificing—all to provide an implausible, melodramatic finale that clears the way for the idyllic postscript in which Logan, Beth and Ben become a family.

It’s understandable, therefore, that Ferguson gives a terrible performance. But the rest of the cast isn’t far behind. Schilling is monochromatic and stiff, Danner relentlessly upbeat and Stewart too cute by half. (In a movie with so many dogs around, its unforgivable that director Scott Hicks—who lingers over every scene as though he were filming a story of Shakespearean gravity—uses the boy as the reaction-shot equivalent of the puppy employed for the same purpose in other movies. He’s abetted in his work by cinematographer Alar Kivilo, who drenches all the widescreen images in a gauzy burnished glow, being certain to capture every glint of sunlight in beads of rain and water.)

But it’s Efron who’s used particularly badly. It seems that apart from his manic, charmless turn as a deliveryman in Garry Marshall’s “New Year’s Eve,” the actor is intent on overcoming his teen heartthrob image by taking parts that require him to be gloomy and intense. “Charlie St. Cloud” started the trend, and now Logan continues it. Efron plays the guy as though he were a zombie who perks to life only when he can help somebody. It’s a dreary performance, though some female viewers—who will doubtlessly make up the majority of the audience—will probably swoon over the bedroom scene in which he strips down to his shorts. The camera certainly does, and Mark Isham’s sappy score certainly gets worked up over it.

If you’re a fan of the formulaic Harlequin-quality drivel that the Sparks produces, this movie should satisfy, and that might make the tearjerker a smash. But it’s hardly a lucky choice for Efron, and certainly isn’t for those of us who prefer genuine emotional depth to manipulative mawkishness.