As legend has it, three Pixar animation chiefs gathered in 2004 at company headquarters, raided the liquor cabinet and hatched a practical joke.

"We can get people to watch anything," said Incredibles director Brad Bird, sloshing his giant glass. "Hey, what if I made a movie about a chef who can't get work in any kitchens, because he's a rat?"

"Good one, Brad," slurred Finding Nemo creator Andrew Stanton. "I'm going to make a movie about a robot who has no friends. Kids'll love that shit."

"OK, OK, how about this?" interjected Monsters Inc. auteur Pete Docter from the floor, where he had briefly passed out. "I'll do a movie about a grieving widower who flies away in a balloon-filled house because he always promised his wife they'd go to South America and he doesn't know how to cope now that she's dead!"

Silence ensued. "Damn, Pete," Bird finally said. "That's dark, even for you."

So, I made that legend up five minutes ago. But some inspiration has made Pixar's last three pictures—Bird's Ratatouille, Stanton's WALL-E and now Docter's Up—increasingly outlandish and…well, sad. Cartoons may possess an ingrained tendency for cuteness, but not since Disney drew Dumbo has a studio so skillfully exploited the medium's capacity for pathos. Pixar's recent heroes have been so frankly vulnerable, so incapable of disguising their loneliness, that they instantly break down the emotional defenses of an audience. Aw, who am I kidding? They break down my defenses: I spent much of WALL-E on the cusp of tears, and started bawling within the first five minutes of Up, pausing only to take notes.

In my defense, the prologue of Up is uncommonly poignant. A little boy with huge hornrims sits agog at a 1930s movie-palace newsreel of South American adventure, then meets a little girl who is equally delighted by tales of discovery. In a montage set to Michael Giacchino's elegiac piano score, the two kids grow up, marry, grow old. They never quite make it to the jungle of their nickelodeon dreams. She slips away in a hospital bed, and Carl—the boy's name is Carl—has become the forlorn old coot Mr. Fredricksen, his voice growled by Ed Asner, his house besieged by progress he doesn't understand. (With his rectangular face, Carl is literally a square.) When he dodges an impending nursing-home confinement by packing his house with rainbow-hued helium balloons, he's making an escape, but also retreating into a floating shrine to his late wife. No wonder the movie's Venezuelan-plateau destination is borrowed from Sir Arthur Conan Doyle's The Lost World: Carl is longing for an existence that cannot be recovered.

Fortunately for Carl, Up also bears a resemblance to Clint Eastwood's Gran Torino—minus the racism, of course. Hiding under Carl's suddenly airborne porch is Russell (Jordan Nagai), an indomitable Wilderness Explorer Scout who looks like a thumb and sounds like the missing Asian cast member of A Charlie Brown Christmas. What adventures the reluctant mentor and his charge run into I won't spoil (the talking dog is an improvement on Bolt's hamster, which is saying something), though I will gripe that Pixar's weakness for third-act chase scenes is not helped by the addition of 3-D, which offers the temptation for even longer chase scenes with rock formations falling toward the camera.

This quibble aside, whatever brainstorming session came up with Up allowed Docter and co-director Bob Peterson to grapple not only with old age, but with the kind of maturity rarely broached by cartoons. A follow-your-bliss greediness is the standard lesson of kids' movies, whether it's the acorn-hoarding of a squirrel in Ice Age or the ambitions of his more sophisticated cousin in Ratatouille. In Up, Carl seeks buoyant happiness, but can only find it when he lets his past float away in order to care for another abandoned kid. The child is father of the man, yes—but it's only by putting away childish things that the man can be father to a child. Damn, Pete. I'm sure there's a lesson there—I'd find it if I could stop crying.

SEE IT:

Up is rated PG. It opens Friday at Eastport, Cornelius, Division, Evergreen, Hilltop, Lake Twin, Lloyd Center, Oak Grove, Sandy, Wilsonville, Cinetopia and Roseway.