The full story
The Guardians have settled on Knowhere, rebuilding the severed Celestial head into a home for misfits and refugees. Peter Quill is drinking himself into oblivion, grieving the Gamora who loved him—because the 2014 Gamora who survived Endgame doesn't know him at all. She left. He's stuck.
Then Adam Warlock attacks.
The Sovereign's golden weapon, teased since Vol. 2, nearly kills Rocket. The damage is catastrophic, but worse: Rocket has a kill switch embedded in his body. Any attempt to heal him triggers it. To save their friend, the Guardians need the code to disable it—and that means finding Rocket's creator.
The High Evolutionary is one of Marvel's most disturbing villains. He's not conquering for power. He's "improving" species, splicing and engineering and discarding failures in pursuit of a perfect society. Counter-Earth—his current project—is populated by animal-human hybrids living in a 1950s suburban nightmare. When they don't meet his standards, he destroys them. All of them. He's done it before. He'll do it again.
Rocket's origin unfolds in flashbacks. Subject 89P13. A baby raccoon, experimented on, given intelligence and consciousness, befriended by other test subjects: Lylla the otter, Teefs the walrus, Floor the rabbit. They dreamed of the sky together. When Rocket showed too much potential, the High Evolutionary decided to dissect his brain. Rocket tried to escape with his friends. The Evolutionary killed them all. Rocket alone survived, carrying that trauma ever since.
The present-day rescue mission takes the Guardians through the Evolutionary's various projects. Nebula and Drax find thousands of children being prepared for the next Counter-Earth. Mantis discovers her own strength. Groot becomes a warrior. And Gamora—this Gamora—slowly understands what this family meant to the version of her that died.
The climax is the Guardians storming the Evolutionary's ship while it prepares to incinerate Counter-Earth. Ayesha dies in the attack, but it isn't her death that turns Adam Warlock—it's the mercy Groot and Drax show him after his defeat. Peter nearly dies in space reaching Gamora; Adam, repaying that mercy, saves him. Rocket faces the Evolutionary directly, choosing mercy where he could have chosen murder. The children and animals are saved. The Evolutionary is left broken in his burning ship.
But the Guardians end.
This is goodbye. Mantis leaves to find herself. Drax stays on Knowhere with Nebula to raise the rescued children—he was always meant to be a father. Gamora returns to the Ravagers; she's not the Gamora Peter loved, and she needs her own life. And Peter? He finally goes home. Back to Earth. Back to his grandfather, still alive after all these years.
Rocket becomes the new captain. Groot, Kraglin, Adam Warlock, Cosmo, and Phyla join his crew. The Guardians continue, but different now.
"I love you guys."