In 2022 New York City, food and housing are extremely scarce because the population has risen to over forty million people. Because of the environmental effects of excessive pollution, most plants and animals have died out, leaving people to consume a manufactured plankton-based product known as Soylent with varieties in red and yellow, and a new high-protein version in green. Police detective Thorn shares a tiny apartment with aged Sol Roth, a former university professor and now police “book” who conducts research to aid Thorn’s investigations. One morning over breakfast, while Thorn urges Sol to expedite information to close his latest two cases, Sol embarks on a familiar rant that when he was a boy, food was sold in stores and people could eat fresh vegetables and real meat. Later, Thorn crawls over several sleeping people on the stairway on his way to a crowded street filled with abandoned, rotting cars and crowds of pedestrians. A mysterious government representative meets with assassin Gilbert in one of the empty cars, providing him with a metal meat hook. At the luxurious Chelsea Towers West apartments, retired attorney and board member of the Soylent Company William R. Simonson presents his companion Shirl with a computer game. Shirl and bodyguard Tab Fielding then depart for supplies and visit an underground black market where Shirl acquires a solitary piece of meat. Meanwhile, Gilbert slips undetected into Chelsea Towers and confronts Simonson. Relating a message of apology and explanation from his employers telling Simonson that he has become unreliable and dangerous, Gilbert then kills the unresisting older man with the meat hook. Later that evening, Thorn assumes investigation of the murder and learns from building manager Charles that the security monitors had recently broken down for the first time in years. Thorn then questions Shirl, who is known as “furniture,” a woman who is contracted with the accommodations. Shirl reveals Simonson was a kindly man, lately depressed, involved in politics and associated with the current governor, Santini. Thorn returns home to present the stunned Sol with sheets of real paper, pencils, an onion, an apple, whiskey and beef, all pilfered from Simonson. Thorn then gives Sol two volumes of the Soylent Oceanographic Survey Report from 2006 and 2015 and urges him to learn all he can about the murdered man. That afternoon, Thorn reports to police headquarters and chief detective Hatcher. Reluctantly admitting he cannot close out one of his pending cases, Thorn nevertheless strongly disagrees when Hatcher suggests providing him with a new “book,” citing Sol’s age. Turning to his new case, Thorn states his suspicion that Simonson was assassinated, citing the unusual surveillance system failure, lack of anything stolen and the intentionally crude murder weapon, a support for his theory, then suggests Fielding’s involvement. Following Fielding later, Thorn goes into a guarded apartment building, but upon reaching Fielding’s room, finds only Fielding’s companion, Martha Philips. After admiring the spacious apartment, Thorn leaves, surreptitiously taking a spoon covered with a red substance. At home, Thorn discovers Sol has utilized the stolen food to make a remarkable meal. Over dinner, Sol reveals that Simonson’s biography noted that he worked for a large legal firm related to the Santini family. Later, Simonson became director of a food freeze-drying company that was eventually bought by Soylent, in which Simonson became a high-standing board member. Afterward, Thorn gives Sol the spoon taken from Martha and Fielding’s apartment and the old man identifies the substance as strawberry jam, which sell for $150 a jar. Returning to Chelsea Towers, Thorn is surprised to find Shirl entertaining several women from the building. Taking Shirl to the bedroom, Thorn reveals that Simonson was murdered and Shirl discloses that Simonson had recently taken her to a church where he prayed with a priest. Later, after the others have departed and Thorn and Shirl have sex, Shirl urges him to remain and take advantage of the hot shower and fresh soap. That night Thorn visits the church and questions the exhausted Father Paul, who will only admit that the truth weighs upon him. The next morning, Thorn returns to headquarters where Hatcher orders him to sign off on the Simonson case, admitting that he has been pressured to do so by the government. Angrily refusing, Thorn departs only to recall he has been assigned to riot duty for the weekly distribution of Soylent Green. Meanwhile, when Santini learns of Thorn’s meeting with the priest, he authorizes any action necessary and that afternoon, Fielding murders Father Paul in his confessional. By late afternoon the Soylent Green supply has been exhausted, infuriating thousands who have waited all day in vain for their portion. While Thorn joins the other police in restraining the crowds, Gilbert pushes his way toward him. As large trucks called scoopers arrive to literally shovel people up, Gilbert fires at Thorn several times, inadvertently killing bystanders. Thorn struggles through the crowd to catch Gilbert who manages to wound the detective in the leg, before accidentally falling under a crushing scoop. Thorn then goes to Fielding’s apartment and, as Martha watches with horror, beats him up, revealing he knows that Fielding must be working for Soylent if he can afford the price of strawberries. Later, Thorn goes to Chelsea Towers where Shirl bandages his leg and laments the arrival of a new tenant. Meanwhile Sol takes the two survey volumes to the Supreme Exchange, a storehouse of the last remaining books and newspapers from the past. Upon learning that the books reveal why Simonson was eliminated, the Exchange Leader tells Sol they must have proof before they can present the information up to the international record keepers, known as the Congress of Nations. Despondent but resigned, Sol goes to a clinic where he will be euthanized while provided peaceful, personally tailored last moments of music and visuals. Arriving home and reading a farewell note from Sol, Thorn rushes to the clinic where he demands to see his old friend. Restricted to standing outside Sol’s private room, Thorn is astonished to see huge screen images of wildlife, plants, birds, fish and nature displayed for Sol’s final moments. Touched by Thorn’s presence, Sol tells him that the images show how the world was once, then relates his knowledge about Simonson and, as he dies, begs Thorn to take proof to the Exchange. Stunned, Thorn secretly follows Sol’s body as it is transported to a waste disposal utility where, along with thousands of other bodies, it is converted into Soylent Green. After fighting off two facility guards, Thorn returns downtown, but finds suspicious men lurking around the Exchange entrance. Thorn tries to phone Hatcher, but when he cannot get through, calls Shirl to tell her to forget him and stay with the new tenant. Thorn is then connected with Hatcher and manages to ask for help before being chased away by several men led by Fielding. Thorn seeks refuge in the church, but Fielding follows him inside, where he severely wounds the detective before Thorn stabs him to death. Hatcher and the police arrive in time to arrest the others. As he is carried away, an overwrought Thorn howls in despair that that Soylent Green is made from people.