Full story
Shortly after the first film, the Guardians are working for the Sovereign, a gold-skinned, snobby people. They fight a monster to protect some valuable batteries while Baby Groot dances. As payment they get Nebula, caught trying to steal. But Rocket swipes a few batteries. High Priestess Ayesha sends a fleet after them, and their ship crashes on a planet after a mysterious man wipes out the attackers. He introduces himself: he is Ego, Quill's father, along with the shy Mantis, who can feel other people's emotions through touch.
Ego takes Quill, Gamora and Drax to his planet. Rocket and Groot stay behind to fix the ship and guard Nebula. Ayesha hires Yondu and the Ravagers to bring the group in. They catch Rocket, but Yondu hesitates to hand over Quill, the boy he raised. The crew mutinies under Taserface, with help from Nebula, who shoots Yondu. His loyal men are killed. Kraglin regrets it and helps Rocket, Groot and Yondu escape, blowing up the ship with Yondu's whistle-controlled arrow.
On the planet, Ego explains that he is a Celestial, an ancient being who built his own planet around himself. He teaches Quill to tap into his inherited power, and they play catch with a ball of energy. Gamora is suspicious, and Nebula arrives to kill her. After a fight, the sisters make peace: Nebula reveals that Thanos took her apart every time she lost to Gamora. Mantis tells Drax that Ego's other children are dead and Quill is in danger.
Ego lays out his plan: he planted seedlings of himself on thousands of worlds and wants to cover everything with his own matter. For that he needs another Celestial. He fathered many children and threw away the ones without the power. Worse, he admits he put the tumor in Quill's mother's head. Quill turns on his father. The Guardians regroup with Yondu, Rocket, Groot and Nebula and take on Ego while his seedlings swallow cities.
Rocket builds a bomb from the stolen batteries, and Groot carries it to Ego's brain at the planet's core. Quill holds his father off with his inherited power until the blast. Ego dies and Quill loses his powers. As the planet falls apart, Yondu gives Quill the only spacesuit and dies in the vacuum. Quill realizes Yondu was his real dad. Nebula leaves to kill Thanos. At Yondu's funeral, Ravager ships fill the sky with fireworks to honor him, and Mantis joins the team, with Kraglin along for the ride. In the credits scenes, Ayesha creates a new being to destroy the Guardians, and Groot shows up as a teenager.