Full story
The Guardians of the Galaxy now live on Knowhere, which they've rebuilt. Quill has been drinking hard since he lost Gamora. One morning, Adam Warlock, a golden warrior created by the Sovereign, storms in looking for Rocket. Nebula wounds him and he flees, but Rocket is left near death. When they try to heal him, a device hidden in his body, a kill switch, nearly finishes him. The only way out is the code to shut it off, kept at Orgocorp, the company that made him.
While Rocket is out, the film goes back into his past. Rocket was a baby raccoon experimented on by the High Evolutionary, a scientist obsessed with creating perfect beings for an ideal society, Counter-Earth. In his cage, he befriended other altered animals: Lylla the otter, Teefs the walrus and Floor the rabbit. Rocket turned out to be smarter than his maker and even fixed his mistakes. Furious, the High Evolutionary decided to harvest Rocket's brain and get rid of the others. Rocket tried to escape with his friends, but they were killed in front of him. He mauled the High Evolutionary's face and got away.
In the present, the Guardians break into Orgocorp with help from the Ravagers. Among them is Gamora, the 2014 version, who doesn't remember Quill and wants nothing to do with him. They get Rocket's file, but the code was removed by Theel, one of the High Evolutionary's aides. The trail leads to Counter-Earth, a planet copied from Earth and full of Humanimals. There, Quill, Drax and Mantis end up on the villain's ship. Nebula, Gamora and Groot try to save Rocket. They pull the code out of Theel's body and restart Rocket just in time. On the edge of death, Rocket sees Lylla, who tells him it isn't his time yet.
The High Evolutionary destroys Counter-Earth and gets ready to try again at a perfect world. The Guardians storm his ship to save the children and animals he keeps locked up. For the first time, Rocket owns his name and his story. He faces his creator but spares him. Mantis and Drax rescue the kids, Groot guards the retreat, and everyone escapes to Knowhere across a makeshift bridge. Quill nearly dies in the vacuum of space, but Adam Warlock saves him.
In the end, the team splits up. Quill hands leadership to Rocket and goes back to Earth to see his grandfather. Mantis leaves alone to figure out who she is, Gamora returns to the Ravagers, and Nebula and Drax stay on Knowhere to look after the kids. In the mid-credits scene, a new Guardians lineup, with Rocket, Groot, Kraglin, Cosmo, Adam and one of the kids, heads out on a mission. In the final scene, Quill has breakfast with his grandfather, and a title card says the legendary Star-Lord will return. When is left open.