Will Smith has played an alcoholic superhero, a mystical caddie and a fighter pilot on a mission to save the planet from aliens, but Ben Thomas, the guilt-ridden do-gooder at the heart of Seven Pounds, might just be the most unbelievable role of them all.

When we meet Ben, a few things about him seem immediately clear. He attacks his job as an I.R.S. tax collector with an exuberance that some might consider grounds for harassment. He is rich beyond reason, though the source of his income remains a mystery. (Government work simply doesn’t pay that well, even in the executive office.) And while he spends his days plotting to help the needy – a blind pianist here, an abused wife there – nothing seems to bring a smile to his face. There is pain lingering behind his plaintive brown eyes, and his melancholy monotone suggests a man who has barely survived some unspeakable tragedy.

Ben meets Emily (Rosario Dawson), a wedding-invitation designer with a heart of gold that is quickly corroding thanks to a congenital condition. Her rare blood type makes a transplant unlikely, but Ben is undeterred. He takes to helping her with odd jobs, walking her Great Dane and weeding her garden. A romance seems inevitable, but Ben remains curiously detached, either unwilling to make the first move or unmoved by her obvious affections.

Why? What is Ben’s connection to Emily, or to the soft-spoken pianist (Woody Harrelson) he cruelly berates on the phone? Where does his money come from? Why does he keep his brother (Michael Ealy) and best friend (Barry Pepper, on hand to provide timely histrionics) at arm’s length? Why are they in this movie at all?

But I digress. Seven Pounds raises so many questions that to list them all would require far more space than I am willing to devote to them. (Even understanding its title demands a small bit of detective work.) Suffice it to say that Ben has his reasons, most of which are hurriedly explained – some satisfactorily, some not – during a whirlwind denouement that tugs at the heartstrings a bit too vigorously. Ben, it turns out, may not be the guardian angel he first appears, but his maudlin odyssey is so far-fetched it just might be otherworldly.