Searching for a way to address overpopulation and global warming, Norwegian scientist Dr. Jørgen Asbjørnsen develops "downsizing", an irreversible process that shrinks organic material. He becomes part of the first group of human test subjects and is encouraged that the process reduces people to a height of approximately five inches[a], drastically decreasing their consumption and waste. When the findings are revealed at a conference five years later, there is a global sensation.Ten years later, Paul and Audrey Safranek, a financially-struggling married couple in Omaha, see Dave and Carol Johnson, who have downsized, at Paul's high school reunion. Rather than the touted environmental benefits, Dave argues the real reason to downsize is that one's money goes much further when one is small. Paul and Audrey decide to undergo the procedure and move to Leisureland, New Mexico, one of the fancier communities for small individuals. In a recovery room in Leisureland, Paul receives a call from Audrey, who says she decided to not go through with their plan and, because they are now different sizes, she is leaving him.One year later, Paul signs his divorce papers. He has moved into an apartment, since he can no longer afford to live in the mansion Audrey picked, and is working as a customer service representative for Lands' End, since he let his occupational therapy license lapse because he had not expected to have to work after being shrunk, but has started dating someone. They break up, however, and Paul attends a wild party hosted by his shady, but affable, neighbor Dušan.The next morning, Paul recognizes one of Dušan's house cleaners as Ngoc Lan Tran, a Vietnamese political activist who was jailed and downsized against her will, escaped in a television box, barely survived being shipped to the United States, and was brought to Leisureland a year ago to have her leg amputated. Wanting to assist Ngoc Lan with her prosthetic leg, Paul goes to her apartment in the slums just outside the walls of Leisureland where the service workers of the community live. Paul had not thought about this part of the small economy, and is shocked by conditions in the slum.At her apartment, Ngoc Lan has Paul try to help her dying friend. When she finally lets him work on her prosthetic leg, he breaks it, so, until she can get a new one, he agrees to work for her cleaning service and also help her gather food from around the city to distribute throughout the slums. Dušan, upon learning what Paul is doing, attempts to release Paul from his obligation by taking him to deliver supplies to the original colony for small people, but, unexpectedly, Ngoc Lan decides to tag along, as she has a standing invitation to visit Dr. Asbjørnsen, who had heard about her ordeal.In a Norwegian fjord, Dr. Asbjørnsen and his wife board the boat piloted by Dušan's friend Joris Konrad. Dr. Asbjørnsen announces it has just been determined conclusively that, due to the positive feedback of Arctic methane emissions,[b] the human race will soon become extinct. Paul asks if downsizing can save humanity, but Dr. Asbjørnsen says the procedure came too late, as only three percent of the world has so far chosen to downsize. That night, Paul and Ngoc Lan make love.At the colony, the travelers discover that, the next day, Dr. Asbjørnsen is enacting a contingency plan: he and the other colonists are going to enter a large underground vault, and their descendants will emerge when the surface environment stabilizes in about eight thousand years. Dušan and Joris are skeptical of the cult-like plan and say the extinction will not happen for hundreds of years, while Paul is excited to enter the vault and help with this effort to ensure the future of humankind. He asks Ngoc Lan to join him, but she refuses, saying the people in need of help will be those left above ground. As the door of the vault is closing, Paul changes his mind and steps outside.Back in Leisureland, Paul continues to work with Ngoc Lan to serve the people of the slums, deriving contentment from things like bringing dinner to an old man.