In Venom: The Last Dance, Eddie Brock and Venom plan on travelling to New York City where they can clear the former's name after he's blamed for Detective Pat Mulligan's death.
When Venom brought Eddie back from the dead in 2018's Venom, a Codex was created that reawakened Knull, God of the Symbiotes. He wishes to destroy everything and sends his Xenophage across the universe to retrieve the "key" created by Eddie and Venom's bond that will free him from his prison on Klyntar.
Meanwhile, a shadowy military organisation has been collecting Symbiotes at Area 51 where they're studied by Dr. Payne and guarded by a reluctant General Rex Strickland.
After being pursued through the Nevada desert and Las Vegas, Eddie and Venom are captured and separated. Mulligan was abandoned by his Symbiote, but is saved by another of the aliens in the military's collection and becomes an easy source of exposition throughout the movie.
However, when the Xenophage attack, Toxin is killed immediately and the other aliens bond with mostly random security guards and scientists to help fend off the invading creatures and buy Venom the time he needs to escape (he and Eddie are reunited by a helpful, Christmas-loving scientist who briefly suits up as She-Venom before getting her own suit).
An epic battle ensues which sees most of the Symbiotes die in battle courtesy of Knull's army. As for Dr. Payne, she becomes the electrically charged Agony; the scientist was struck by lightning as a child in an accident that killed her brother.
Venom and Eddie realise they must make the ultimate sacrifice to save the world and keep Knull in his prison. After healing his host's wounds, Venom forcibly expels his host and attaches himself to the surrounding Xenophage. Growing massive in size, the Symbiote pulls them to a nearby machine the military has been using to destroy Area 51's secrets with acid.
At Venom's prompting, Rex douses Venom and Knull's army in the deadly substance and, with his final act, Venom makes sure to save Eddie after an emotional farewell (Rex, meanwhile, blows himself up to help finish the job).
Back on Klyntar, Knull senses the destruction of his Codex and screams in rage as he remains trapped in his prison.
With that, Venom is dead and Eddie's name is cleared as thanks for his heroic actions. Earlier in the movie, Venom had talked about wanting to see the Statue of Liberty so Eddie - walking through New York as a montage of his and Venom's best moments plays - makes good on that by travelling to the Big Apple and taking it all in for his fallen friend.
Of course, the post-credits scenes at least hint that Venom might return. You can read about that by clicking here.