In the year 2022, the cumulative effects of overpopulation, pollution, and some apparent climate catastrophe have caused severe worldwide shortages of food, water and housing. There are 40 million people in New York City alone, where only the city's elite can afford spacious apartments, clean water, and natural food, and even then at horrendously high prices. The homes of the elite usually include concubines who are referred to as "furniture" and serve the tenants as slaves.

Within the city lives NYPD detective Frank Thorn and his aged friend Sol Roth, a highly intelligent analyst, referred to as a "Book". Roth remembers the world when it had animals and real food, and possesses a small library of reference materials to assist Thorn. Thorn is tasked with investigating the murder of the wealthy and influential William R. Simonson, and quickly learns that Simonson had been assassinated and was a board member of Soylent Industries.

Soylent Industries, which derives its name from a combination of "soy" and "lentil", controls the food supply of half of the world and sells the artificially produced wafers, including "Soylent Red" and "Soylent Yellow". Their latest product is the far more flavorful and nutritious "Soylent Green", advertised as being made from ocean plankton, but is in short supply. As a result of the weekly supply bottlenecks, the hungry masses regularly riot, and they are brutally removed from the streets by means of police vehicles that scoop the rioters with large shovels and dump them within the vehicle's container.

With the help of "furniture" Shirl, with whom Thorn begins a relationship, his investigation leads to a priest that Simonson had visited and confessed to shortly before his death. The priest is only able to hint at a gruesome truth before he himself is murdered. By order of the governor, Thorn is instructed to end the investigation, but he presses on. He is attacked during a riot, by the same assassin who killed Simonson, but the killer is crushed by a police vehicle.