Leave it to the vision masters at Pixar to take a fairly grim sounding story about a cantankerous old widower staring down his fading years and turn it into a charming, buoyant, life affirming piece of entertainment for all ages.

Carl Fredrickson is introduced in the opening credits as a blocky little post-depression-era ragamuffin, hopped up on Saturday morning serials and news reels depicting the exploits of his hero, the intrepid archeologist/pilot/explorer Charles Muntz. Skipping home from the picture house, balloon in hand, sidewalk cracks become Grand Canyons and tree stumps the peaks of the Himalayas. Happening upon a plucky young lady of like imagination in an abandoned old ramshackle house she’s turned into a rickety model of Muntz’s famously posh airship “The Spirit of Adventure,” Carl finds his first friend, his true love and, as an ensuing (and positively sublime) 10-minute montage illustrates, a partner with whom he shares a wonderful and joyful, if domesticated, life.

They grow up, marry, buy that ramshackle clubhouse and fix ’er right up. They make a modest living together selling balloons at the zoo. Having pledged as children to follow their hero one day on an adventure into the South American jungles of a very Miltonesquely named “Paradise Falls,” we see their intentions perennially deferred to the responsibilities of the ordinary, their savings jug of pocket change repeatedly smashed open over the years to cover costs of flat tires, household repairs and, eventually, medical bills.

One of the great successes of this story is how firmly rooted it is in real world concerns. Unlike most toons, when these characters hit the ground, their bones break. They go to the hospital. Their adversaries manifest, in the most grounded and human of ways, as uncertainty, infirmity and, in an astonishingly heart wrenching turn, infertility, illness and death. Oscar winning writer/director Pete Docter (“Monsters Inc.”) shows deft shorthand in relating the depth of Carl’s affection for his darling wife Ellie, and the subsequent profundity of his grief with her loss. Though he weaves in all the bright child-friendly colors one would expect from a 3-D animated family film, Docter doesn’t shy one whit from adding some exceptionally grownup themes.

It comes as a fair shock in this medium when, as his beloved home is being swallowed by urban development, lonely old Carl’s temper is challenged by a well intentioned laborer, and an irate cane-crack to the head results in actual blood flow (a Pixar first). And again, unlike most toons, there are real consequences. Carl’s taken to court and is ordered into the care of a rest home.

And here’s where reality takes a back seat and the real fun begins. With nothing left to lose, Carl thumbs his nose at the world, inflates his whole back stock of balloons and flies his house right the hell out of town. Setting course elatedly for Paradise Falls, he’s surprised to find a stowaway onboard—an eager young scout looking to earn his final badge (in assisting the elderly) who was trapped on the porch at liftoff.

Carl’s reclusive reluctance to accept the uninvited company eventually gives over to a begrudging paternal instinct, and the unlikely pair soar off together to the ends of the world.

Finding themselves on the other side of a formidably Dorothy-level gale, their journey takes another fabulously mature turn, as Carl’s meticulously crafted sentimentality for the past becomes a burden he literally must drag around on his back. Falling a few miles short of his mark, he fashions a harness of the house’s garden hose and proceeds to haul the home through the wilds, and as the balloons start to pop, the building grows steadily more cumbersome.

If there’s any shortcoming at work in “Up,” it could simply be an ambient predictability. Once on the plateau, they inevitably discover an ancient Charles Muntz, who, having gone a little “Dr. Moreau” in his 60-odd-year exile with his pack of sinister talking dogs, still obsessively stalks a particularly elusive species of giant bird. The following action adventure, as Carl and his newly found surrogate son go toe to toe with the old hunter, is as rousing and creative as anything Pixar has done before, and though maintaining a healthy grip on the emotional underpinnings of the first act, fails, if only slightly, to completely live up to its promise.

There are plenty of exciting surprises to distract from this, however, including a genuine aerial dogfight, a little bit of cane-play swashbuckling, and an instance of comeuppance (or, in this case, comedownance) that breaks one of Pixar’s heretofore cardinal rules. You’ll know it when you see it.

Overall, Pixar can proudly notch its belt for yet another brilliantly crafted fable for modern times. The movie shows great care to visually match tone, texture and depth of field to the nuances of fully realized and often hilarious characters—all attempting to hold onto their dreams while learning that true adventure, embracing potential, and exploring the promise of new dreams over the old is ageless. Turns out, if you really want your balloons to fly, you must learn to let them go.