The Namek Saga was the second Saga in Dragonball Z. The Namek Saga is one of the longest sagas in Dragonball Z and has from when Vegeta is beaten to when Goku arrives on Namek. I have a list of the episodes and a summary of everything that happens in it. The Namek Saga has episodes 27-53 in it.
Goku continues to fight Burter and Jeice. The two famed warriors of the Ginyu Force are quickly defeated. In an act of mercy, Goku lets them go rather than finishing them off. Jeice flees to Frieza's to get help from Captain Ginyu. Vegeta gets angry at Goku for being too soft and hits Burter with a deadly blast.
Frieza tries to summon the Namekian Dragon, Shenron, and nothing happens. After this failed attempt, Frieza heads to Guru's to find out how to use the Dragon Balls.
The battle is far from won. Captain Ginyu, head of the Ginyu Force, arrives. Goku and Captain Ginyu face off in battle. Captain Ginyu quickly realizes Goku is stronger, and surprisingly stabs himself. Unaware of what's about to happen, Goku's caught in a strange beam of light. Captain Ginyu has used his "metamorphosis" attack and switched bodies with Goku.
Krillin and Gohan arrive at Frieza's ship to locate the Dragon Balls and summon Shenron. Vegeta also shows up, but hides to let Gohan and Krillin locate the balls with their Dragon Radar. Nothing happens when they try to summon the Dragon. Gohan and Krillin sense someone coming and hide.
Jeice and the "new" Goku arrive at Frieza's ship wondering who dug up the Dragon Balls. Krillin mistakenly comes out to greet Goku, and soon realizes this is not the Goku he knows. Gohan and Krillin begin fighting Jeice and "Goku", then the real Goku arrives in Captain Ginyu's body. The real Goku reasons with Krillin and Gohan that they can beat this "Goku" because he isn't used to his body and won't know how to use all of its powers. When Captain Ginyu in Goku's body is almost defeated, Jeice comes out to help. Vegeta also comes out of hiding to take on Jeice. Vegeta easily defeats Jeice. Captain Ginyu, tired of Goku's body, tries to sneak in another metamorphosis attack to switch bodies with Vegeta. The switch is stopped when Goku (in Captain Ginyu's wounded body) jumps in front of Vegeta and gets his body back. Captain Ginyu tries to switch with Vegeta again, but this time is stopped when Goku throws a frog up to stop the beam from reaching Vegeta. Before anyone knows what is happening, Captain Ginyu is trapped in a frog's body. Goku is put in the rejuvenation chamber on Frieza's ship. This battle is over.