The full story
Venom: Let There Be Carnage opens on Eddie Brock and Venom living in uneasy cohabitation. Venom is restless—confined to their apartment, forbidden from eating people, surviving on chocolate and live chickens. He wants to be a hero. Eddie wants to rebuild his journalism career. They argue constantly, like a married couple who can't agree on anything except that they need each other.
Detective Patrick Mulligan enlists Eddie to interview Cletus Kasady, a death-row serial killer at San Quentin who refuses to speak to anyone else. Kasady is obsessed with Eddie and sees a kinship between them. During one visit, Kasady bites Eddie's hand hard enough to draw blood—and ingests a trace amount of symbiote-infused blood. This seeds a new symbiote within Kasady.
Eddie's interview notes lead police to the bodies of Kasady's victims, earning Eddie a career revival but enraging Kasady, who feels betrayed. When Kasady is subjected to lethal injection, the symbiote activates. Carnage erupts from Kasady's body—a red, chaotic, larger symbiote that makes Venom look restrained. Kasady and Carnage break out of prison, slaughtering guards.
Carnage frees Frances Barrison (Shriek), Kasady's childhood love, from the Ravencroft Institute. Frances has sonic-scream powers—a dangerous complication since symbiotes are vulnerable to sound. Kasady and Frances plan a twisted "red wedding" at a San Francisco cathedral.
Meanwhile, Eddie and Venom have their worst fight. Venom, feeling unappreciated and constrained, separates from Eddie and bounces between hosts at an underground rave, briefly experiencing freedom. Eddie, powerless and alone, realizes he cannot face Carnage without Venom. They reconcile—acknowledging that they are better together than apart—and re-bond.
Carnage and Shriek kidnap Anne and Detective Mulligan, luring Eddie to the cathedral. The final battle pits Venom against Carnage in the cathedral's rafters. Carnage is stronger and more violent, but Carnage and Shriek have a fatal conflict: Frances's sonic screams, which she can't fully control, hurt Carnage as much as any enemy. Venom exploits this weakness. In the end, Venom devours Carnage and bites Kasady's head off, killing both.
Eddie and Venom go on the run, hiding in a beachside hotel. Then comes the post-credits scene that connects to the MCU: Venom begins explaining the symbiote hive-mind and its knowledge of a multiverse when reality shifts around them. The hotel room physically transforms. A TV news broadcast shows J. Jonah Jameson revealing Spider-Man's identity as Peter Parker—Tom Holland's face on screen, footage from the end of Spider-Man: Far From Home. Venom surges forward, licking the screen, fascinated. Eddie and Venom have been pulled into the MCU.