Years ago in a cell on Ryker's Island, serial killer Cletus Kasady grins menacingly at his new cellmate – Eddie Brock – and asks if he wants to know why he is going to die. As Kasady mockingly says that the guards are feeding Eddie to him like a mouse to a snake, the guards snap at him to shut up and play nice. As the guards leave, Eddie gruffly tells Kasady that he wants the bottom bunk so that he can keep an eye on him, Kasady agreeing and quipping that Eddie is smarter than his last cellmate, whose death earned him his 11th life sentence. Kasady asks for Eddie’s name, and upon recognizing him as the monstrous super-villain Venom, he gleefully states that they are alike and asks if they could team up. Eddie immediately rebukes him, snapping that they are nothing alike and that he is not an insane serial killer who slaughters innocents. Pulling out his headphones, Kasady grouses that Eddie should not be so rude and reiterates his offer of friendship, grinning wickedly as he says he senses they have a beautiful future ahead of them.
In the present, Eddie – bonded to a gestalt symbiote formed from amalgamated codices – smashes Kasady – bonded to an offshoot of the primordial Grendel symbiote and now going by Dark Carnage – through the wall of an abandoned apartment building. Unfazed, Dark Carnage laughs and says that Knull is almost awake, asking Eddie if he can hear him breathing. Punching Dark Carnage in the face, Eddie snarls at him to shut up and die, but mentally notes that Dark Carnage is right and that, after bonding to the codices, he can feel the symbiote hive mind. Grabbing Eddie by the throat, Dark Carnage snarls that he can hear Eddie too, tossing him through the wall and onto the roof of the building across the street. Hovering over Eddie, Dark Carnage says he can see through the eyes of every member of his horde and sees Eddie’s allies being overwhelmed by Carnage doppelgängers. Landing, Dark Carnage says that he is going to kill Eddie and take his codices, thereby unleashing Knull and bringing ruination to the universe. Gloating, Dark Carnage tells Eddie to give up his codex willingly so that they can rule together; but Eddie snaps at Dark Carnage to shut up, saying that he does not care about Knull or Kasady’s mission to wipe out all life on Earth, he just wants his symbiote back and Kasady back in his grave for good.
As Eddie tells Dark Carnage to take another look at his friends, Cloak teleports into Rex Strickland's Warehouse and uses his cloak to bring Dagger, Iron Fist, Firestar, Morbius the Living Vampire, Deathlok the Demolisher, Captain Marvel, Deadpool, and Scream in as backup. As the tables turn on his horde, Dark Carnage staggers and clutches his head in disbelief, Eddie taking advantage of the distraction to tackle him off the roof.
In the tunnels under Rex Strickland's warehouse, Spider-Man knocks out the Carnageized Norman Osborn, turning to reassure Dylan Brock and Normie Osborn that everything is going to be fine before passing out. Normie asks if Spider-Man is dead, but Dylan says he is just asleep. As he says everything is going to be okay, the offshoot of the Dark Carnage symbiote bonded to Norman detaches from him – Dark Carnage mockingly telling Eddie that he is going to use it to kill Dylan. As Norman's offshoot of the Dark Carnage symbiote looms over them, Dylan snaps that he hates symbiotes, his eyes turning black with red spirals. As Dylan thrusts his hands out, Norman's symbiote is obliterated into a spattered puddle of red and black ooze, Normie incredulously asking Dylan how he did that. Stammering that he does not know, Dylan passes out into Normie’s arms just as Dark Carnage and Eddie crash through the ceiling.
Crawling towards the two boys, Dark Carnage laughs and says that Dylan is the final piece of the puzzle, Eddie grabbing onto his ankle and – retracting the symbiote from his face – shouting that he will not let Carnage kill his son as he tries to restrain his nemesis with tendrils. Laughing sinisterly, Dark Carnage says that Eddie still does not understand that he has already lost – explaining that, between the two of them, they have more than enough codices to awaken Knull. Retracting the Dark Carnage symbiote from his skull-like face, Kasady states that Eddie faces the choice of allowing him to consume Dylan’s codex or killing him to save Dylan and take back his symbiote – but either way, Knull will be unleashed. Eddie realizes that Kasady had planned for him to take the codices from the S.C.I.T.H.E. and place him in a lose-lose scenario, deciding to save his son anyway. Manifesting a necrosword from his symbiote and impaling Dark Carnage with it, Eddie slices him in half; the Dark Carnage and Venom symbiotes leaving Kasady – whose corpse shatters as it falls to the ground - and bonding to Brock. As it rebonds to him and assimilates the Dark Carnage symbiote and the gestalt codices, the Venom symbiote berates Eddie and informs him that Knull has awakened.
Light years away, the planet Klyntar explodes into billions of symbiotes, Knull coalescing them into a fleet of Symbiote Dragons, manifesting a suit of draconic symbiote-armor, and resuming his conquest of the cosmos.
Opening his eyes to the Venom symbiote, asking if he can hear it and begging him to talk to it, Eddie turns to see Spider-Man regaining consciousness. Spider-Man asks if they won, Eddie hesitantly saying that they did. Looking around, Spider-Man wonders where Norman Osborn disappeared to, Eddie saying that he did not notice and that he should get on it. Sighing, Spider-Man says he will do so after checking in on how everyone else is doing, asking Eddie if they are good. Hugging him, Eddie says that they are good, Spider-Man awkwardly saying he is unsure what their relationship is now, but that he has Eddie's back. Taking Normie, Spider-Man leaves and tells Eddie to look after Dylan. Saying he will do his best, Eddie turns to see Dylan staring at him in shock and sits next to him. After several seconds of staring blankly ahead, Dylan asks if Eddie said that he was his son.
