Jason Reitman’s previous films—“Thank You for Smoking,” “Juno,” “Up in the Air,” “Young Adult”—have all been comedies with dramatic—or at least dark—overtones, but though there are some laughs in “Labor Day,” most of them are unintentional. Instead this is a plodding, mushy melodrama in Nicholas Sparks mode, though it’s actually adapted from a novel by Joyce Maynard. Perhaps it represents the writer-director’s attempt to stretch, but if so he’s strayed too far from his comfort zone.

The heroine of the piece is Adele Wheeler (Kate Winslet), an emotionally troubled, agoraphobic divorcee living in a small town in 1987 with her gravely solicitous fourteen-year old son Henry (Gattlin Griffith, though Dylan Minnette and Tobey Maguire step into the role as the lad grows up). On one of their rare shopping trips, the two are accosted by an injured escaped convict named Frank Chambers (Josh Brolin), who forces them to drive him back to their ramshackle house.

This sounds like the setup for a tense hostage drama, but “Labor Day”—which spans the long holiday weekend—turns into something quite different, a tale of a family healed by a savior, because Campbell is no thug. He’s an extraordinarily sensitive, multi-talented fellow whose conviction for murder, as we’re shown in a series of artsy flashbacks (in which the younger Frank is played by Tom Lipinski), is far more complicated than the newspaper headlines and TV news reports suggest. Frank is the ultimate Mr. Fixit. He changes the oil and the tires on Adele’s car; he repairs doors and cleans out gutters; he sees to the timer on the water heater; he washes and waxes the wood floors. And he fixes mother and son, too, drawing both out of their shells by dancing with her and teaching him how to catch and hit baseballs.

And he cooks, beginning with a steaming pot of chili and proceeding—when Jarvis (J.K. Simmons), a helpful neighbor, brings over a bucket of home-grown peaches—to instruct Adele and Henry about the proper way to bake a pie from scratch. This sequence is certainly the picture’s most ludicrous, as Reitman employs the caressing of the squishy fruit and the kneading of the dough as a metaphor for the bonds of intimacy that grow between Frank and Adele. Lovingly shot cuts of the thick-crusted pastry heaving and bubbling in the oven heat mirror the slight sounds of their sexual activity that Henry hears through the wall as he lies awake at night.

Reitman tries to build a bit of suspense as the ridiculous plot proceeds, not only through the sudden appearance of Jarvis with his peaches but that of another neighbor, Evelyn (Brooke Smith), who prevails on Adele to watch her disabled son (Micah Fowler) for the day; at a later point he also introduces a suspicious policeman (James Van Der Beek) for a sequence in which an attempt at Hitchcockian dread (just think of the cop in the first act of “Psycho”) fails to register. The final reel of “Labor Day” goes further in that direction, offering an ill-planned visit to a bank, an effort by Henry to say goodbye to his remarried dad (Clark Gregg) when Adele decides that they’ll escape with Frank to Canada, and the reappearance of Evelyn, who’s confronted by Frank. There’s even an odd subplot in which Henry encounters Eleanor (Brighid Fleming), a world-wise (and wise-cracking) new girl in town who scares the boy by suggesting that his mother might e planning to run off without him but gives him his first taste of romance as well.

But none of these scenes—accompanied, as is the kidnapping sequence at the start, by the throbbing thuds of Rolfe Kent’s uninspired but insistent score—cause the pulse to race, largely because the basic premise of the story is so absurd. Frank loiters about the house, occasionally walking into the yard to do chores, apparently unconcerned about being discovered except when a police car solemnly rolls by on the street outside. (That’s merely one instance of the foolishness with which the three major characters behave.) And Frank is such a saintly guy that, except for the opening abduction scene, creating a real sense of menace is impossible.

The cast is constrained by the material. Winslet is all fluttery fragility, a modern-day Tennessee Williams damaged woman who comes to depend on the kindness of one particular stranger. Another set of flashbacks tell us the reason behind Adele’s condition, which adds a second meaning to the film’s title, but the result is curiously unmoving. Brolin can do little but coast on his natural virility, but he certainly personifies the rock of strength both Wheelers crave. It’s no wonder that both stars seem to heave a sigh of relief when they get to the years-later postscript, in which the grown Henry is also shown to have a job hearkening back to his instructive weekend with Frank. Maguire’s overblown, pseudo-poetic looking-back narration, like most of the film’s dialogue, sounds like words taken from a page rather than spoken by real human beings; and his performance is so stolid that he seems to be sleepwalking. But Griffith uses his big eyes to good effect in the scenes at home, and does affecting work in those with Gregg and Fleming.

On the technical aide, Eric Steelberg’s cinematography is certainly eye-catching, with the hazy widescreen images, in which everything and everyone appear to be surrounded by luminous aureoles of light, reflecting the wooziness of the narrative. The production design (Steve Saklad), art direction (Mark Taylor), sets (Tracey A. Doyle) and costumes (Danny Glicker) do a fine job of creating a period atmosphere that’s effective without being ostentatious about it, but Dana E. Glauberman’s stately editing simply reinforces the solemn directorial tone that italicizes the film’s portentous air.

The material of “Labor Day” is ripe for parody—as ripe as those peaches, in fact. But instead the film plays things ponderously straight. The result might have been a labor of love for Reitman, but for the audience it’s just laborious.