After the fight with Vegeta. A few months pass and now you, Gohan, Krillin and Bulma go to Namek to get the dragon balls to wish Tien, Yamcha, Chiaotzu and Piccolo back. But things are bad. Frieza is invading Namek, Vegeta was also there.

Gohan: "Well. Now we have be careful. When getting the dragon balls since that Frieza guy has some of them."