As Downsizing (which Payne co-wrote with frequent partner Jim Taylor) opens, a group of Norwegian scientists have discovered a way to miniaturize living beings–including humans. The world then begins a 200-year plan of transitioning almost everyone to five inches in height as a way to ease overpopulation and save the world’s increasingly fragile environment, with the downsized moving into specially constructed and seemingly perfect little communities. One incentive is that money goes much further when you live smaller, which tips the scales for struggling Omaha couple Paul and Audrey Safranek (Matt Damon and Kristen Wiig), who decide to go through with the irreversible process. After more or less abandoning the ramifications of the shrinking process and how the outside world sees it, I thought Payne was going to go a little more into his comfort zone and peer into the personal foibles of his downsized community and its denizens. But the movie takes another turn, as Paul meets up first with a pair of dissolute European party people (Christoph Waltz and Udo Kier, alternating between funny and bored), and then falls in with Ngoc Lan (Hong Chau), a former Vietnamese activist who was shrunken by her government as punishment and now cleans houses in Leisureland. Through her, Paul discovers things about Leisureland he didn’t know, while finding perhaps some fulfillment in assisting Ngoc as she helps the community’s less fortunate residents.

Chau brings a needed spark of life to Downsizing at this point, since Damon is more or less morose and brooding throughout, although her character walks a thin, treacherous line between saint and stereotype. She’s irritating at first, grows more endearing, but is ultimately as frustrating as the rest of the movie, which takes one final detour in its final third into a heavy-handed mush of apocalyptic New Agey “spirituality” that stops the movie dead in its tracks and finally sinks it. But no one really escapes this mess unscathed, least of all Payne and Taylor. While they’ve been brilliant before at incisively probing deeply flawed characters (Sideways) and dissecting microcosms of modern society (Election, pretty much a perfect movie), they can’t decide what to do with their characters here and find themselves stumped when exploring a literal microcosm of contemporary American life. While the movie is well-designed in its depiction of its near-future “big” world, the laboratories where the shrinking process takes place and its economy-sized Leisureland, all that creativity comes to naught in the movie’s undercooked story. Perhaps speculative fiction is just not the right genre for this often humane yet snarky filmmaker: Downsizing offers him his biggest conceptual canvas yet, but ironically feels like his smallest movie to date. Downsizing opens in theaters on Friday, Dec. 22.