Downsizing opens in a Norwegian lab where a group of scientists are testing an experimental technique to reduce animals in size. It soon becomes clear that the purpose of these endeavors is to apply the technology to human beings. The most dramatic scene in the film is the moment when the team presents a five-inch person to a lecture hall of astounded researchers and journalists. We then flash forward several years to discover that downsizing has become a popular trend, though the majority of people undergo the procedure for financial rather than piously environmental reasons. It appears that the dollar goes much further when you have tiny clothes, your nutritional needs are those of a mouse, and you live in a doll house.
At this point, we meet Paul Safranek (played by a rather pudgy-looking Matt Damon) and his wife Audrey (Kristen Wiig in a surprisingly sober turn), who have decided to take the plunge. But on the fateful day, Paul goes through with it, while Audrey chickens out, leaving Paul stranded in the land of the tiny. Compelled by his wife’s treachery to divorce, Paul finds himself out of his mansion and stuck in a nowhere-job and a small apartment. Just as he hits bottom (literally lying in a stupor on the floor of a friend’s apartment after a night of debauchery), he spies Ngoc Lan Tran (wonderfully incarnated by Hong Chau), a noble Vietnamese activist who had been forcibly downsized by her government and who now does menial labor, cleaning the homes of the wealthy. Despite the loss of a leg, Ngoc has devoted herself, in her spare time, to the care of an army of the underclass of the small, who live in a sprawling slum. When she discovers that Paul has some basic medical training, she presses him into service, bringing him to suffering person after suffering person, compelling him to come out of himself. Carrying a Bible and attending enthusiastic religious services, Ngoc is unembarrassedly a Christian, and it is unmistakable that her faith informs her dedication to those in need.
More here, but beware of spoilers.