The film, which is loosely based upon the 1966 science fiction novel Make Room! Make Room!, by Harry Harrison, won the Nebula Award for Best Dramatic Presentation and the Saturn Award for Best Science Fiction Film in 1973. In 2022, the population has grown to forty million people in New York City alone. Housing is dilapidated and overcrowded; homeless people fill the streets and line fire escapes and stairways. Food is scarce; most of the population survives on rations produced by the Soylent Corporation, whose newest product is Soylent Green, a small green wafer advertised to contain "high-energy plankton". It is more nutritious and palatable than the other varieties but is in short supply, which leads to food riots. Protagonist Robert Thorn is a New York City Police Department detective living with his aged friend Solomon "Sol" Roth, a former scholar who searches the remnants of written records to help Thorn's investigations. Thorn investigates the murder of William R. Simonson, a director of the Soylent Corporation while helping himself to the latter's food, liquor, bathroom, and books. He questions Shirl, an attractive concubine (referred to as "furniture"), and Simonson's bodyguard, Tab Fielding, who claims to have escorted Shirl shopping when the attack took place. Returning to his apartment, Thorn gives Roth the Soylent Oceanographic Survey Report, 2015 to 2019 taken from Simonson's apartment; then tells his Lieutenant (Hatcher) that he suspects an assassination on grounds that nothing was stolen from the apartment and the murder seemed professional, given that the apartment's sophisticated alarm and monitoring electronics failed to detect the murder and Fielding failed to prevent it.
After questioning Fielding's mistress, Martha, Thorn returns to his apartment. When he presents Roth with strawberry jam taken from Fielding's apartment, Roth declares it too great a luxury for the concubine of a bodyguard. Thorn returns to question Shirl again; whereupon she tells him that Simonson became troubled in the days before his death. Thorn questions a priest whom Simonson had visited but the priest at first fails to remember Simonson and is later unable to describe the latter's confession. Fielding later murders the priest to silence him, suspecting the priest of revealing Simonson's confession to Thorn. When Thorn begins discovering why Simonson was murdered, New York State's Governor Joseph Santini, once Simonson's partner in a high-profile law firm, orders the investigation closed; but Thorn disobeys. When Thorn is on riot duty at the distribution of rations, Simonson's murderer is dispatched by the Soylent Corporation to kill him but the murderer is crushed by a riot-control vehicle. Roth examines Soylent's oceanographic reports; he and his fellows discover that the oceans are barren, no longer producing the plankton from which Soylent Green is said to be made. In fact it is made from people. Unable to live with this discovery, Roth seeks assisted suicide at a government clinic in Madison Square Garden. There, Roth tells Thorn the secret of Soylent Green and begs him to follow his body to the processing center and report to the other scholars.
Thorn does so and sees human corpses converted into Soylent Green. Returning to make his report, he is ambushed by Fielding and retreats into a cathedral filled with homeless people, where he kills Fielding.
When police arrive, Thorn urges Hatcher to spread the word that "Soylent Green is PEOPLE!"
RICHARD FLEISCHER (1973)