Zac Efron makes an affecting and credible dramatic lead in “Charlie St. Cloud,” the movie Nicholas Sparks wishes he could write, based on the book by Ben Sherwood. Like Sparks’ stories, this has loss, and love, and a setting at the shore. But it has more depth, more bite, more humor, than the popular Sparks stories, and is more touching as well.

Efron has shown himself as an agreeable teen idol in the “High School Musical” series, and he demonstrated comic skills in “17 Again” and an an ability to work well in a dramatic ensemble period piece in the under-seen “Me and Orson Welles.” He has chosen wisely, reportedly walking away from a remake of “Footloose” for this film, which makes the most of his natural charm and gives him an opportunity to show off some acting skill as well.

Efron plays the title character, a good kid, just graduating from high school with a world opening up to him. He has a sailing scholarship at Stanford and a chance to leave behind his responsibilities to his overworked mother (Kim Basinger) and kid brother Sam (likable Charlie Tahan). He is devoted to both of them, but as he swings his sailboat around in the first scene to win a race, we can see that even he is not aware of how impatient he is to get on with his life.

But then he and Sam are in a car accident. Charlie almost dies but is brought back by a devoted EMT (Ray Liotta). Sam is killed. Charlie is devastated, shredded with guilt. Five years later, he still hasn’t left town. He is a full-time care-taker at the cemetery where Sam is buried. He keeps to himself. Except that every day at sunset, for an hour, he goes off into a clearing in the woods, where he throws a baseball with Sam.

Charlie can still see Sam. And he can’t let go of him, and of the promise he made to coach him for an hour every day. He is all but ruined by survivor guilt he cannot begin to acknowledge. He feels alive only when he is with Sam.

And then a girl comes back to town. Her name is Tess (Amanda Crew) and she represents everything that is most threatening to Charlie’s cocoon of grief — adventure, travel, life, and romantic love. She is a sailor preparing to go solo around the world.

Screenwriters Craig Pearce and Lewis Colick have adapted Sherwood’s book with a light touch for visual metaphor, nicely handled by director Burr Steers (“Igby Goes Down”) and the exquisite images from director of photography Enrique Chediak. The vigorous dynamism of the sailing scenes contrast with the quiet, static cemetery (even when invaded by geese). The characters represent a range from the vital engagement of the young woman embarking on a solo voyage to the character preparing for his own death by sharing what he has learned.

Efron is genuinely splendid in the early scenes. Charlie has not had an easy life, but he has a natural ease that makes him seem on top of the world. He is a good kid who wants to do the right thing, but he has the impetuousness and carelessness of someone who thinks his time has come. After Sam’s death, Efron’s perfomance becomes more subtle as he shows us Charlie’s uncertainty and isolation. That natural ease has become a shield to keep everyone away. He is comfortable doing his job and living half in the world of the living, half in the world of the dead. When Tess arrives, we see him struggle with longing and the possibility of hope.

And then, just as on that first sailboat race, he takes a turn we did not expect to cross the finish line, leaving us a little breathless at the way it comes together, moved by both Charlie and by Efron and wanting good things for both of them.