Grade: D

The title accurately reflects the wafer-thin quality of “Paper Man,” a flimsy character study about a man-child who finally outgrows the crutches he adopted as a kid to survive—in particularly an imaginary friend—and come to terms with adulthood. But the movie, the debut of the husband-wife writing-directing team of Michele and Kieran Mulroney, itself seems a case of arrested artistic development.

Jeff Daniels, mugging even more than usual, plays Richard, a New York author with a deadline looming over him whose cardiologist wife Claire (Lisa Kudrow), a take-charge person, installs him in an isolated Long Island house where he can overcome his writer’s block, stopping in periodically to make sure he’s surviving without her. The change of locale isn’t much help—Richard spends his time in front of the typewriter (an archaic touch) mulling over variations in an opening line about the virtue of solitude. But he’s not really alone—he’s brought along the invisible-to-everyone-else pal who’s accompanied him since childhood, a spandex-clad, caped superhero called Captain Excellent (Ryan Reynolds), who may be brusque and imperious but is often right in pointing out Richard’s shortcomings.

Despite the captain’s warnings, however, Richard bikes off into town, where he encounters a teen girl, Abby (Emma Stone), who piques his interest. An obviously unhappy kid, she’s bullied by an arrogant boyfriend (Hunter Parrish) and mooned over by a puppy-dog guy (Kieran Culkin). Out of the blue Richard offers her a babysitting job, though there’s no kid to sit. And the bulk of the picture is built around their effect on each other; she brings him out of his shell and he helps her break free of her emotionally abusive b.f. and grow up, too.

There’s the germ of a potentially engaging, and incisive, March-September relationship here (one that’s entirely sexless, incidentally, though the age difference means that there’s a slightly creepy quality to it nonetheless). But the script never manages to make it convincing or enlightening, despite Stone’s strong performance as Abby, which captures both the girl’s rough, often rude manner and her emotional fragility. And a twist at the close concerning Culkin’s mysteriously omnipresent character doesn’t save things.

Even worse, though, is the whole “imaginary friend” aspect of the piece. Though there have been cases where the idea has worked (“Play It Again Sam” is a fine example), it’s basically a tired conceit that more often turns out poorly (just think “Drop Dead Fred”). And here the superhero persona proves a particularly weak link, despite the character’s ability to fly. Simply put, Captain Excellent quickly becomes not just tedious but actually unnecessary to the plot, except as a crutch to the writers as well as the protagonist. And while Reynolds strikes all the right poses, his discomfort with the costume (and the bleach-blond hair) seems to the simmering beneath the surface. Kudrow seems equally ill-at-ease in a really underwritten part.

“Paper Man” has the look of the average independent picture, neither stunning nor ugly, and the score (by Mark McAdam, with additions selected by Robin Urdang) at least avoids becoming the bubbly irritant one hears so often in this sort of whimsical tale. In short, technically it’s as mediocre as it is substantially. It’s a film that wants to get at some relatively profound issues about growing up, but comes off as ephemeral and forgettable as a sheet of paper carried off by a gust of wind. Happily, in this case it’s not much of a loss.