Dragon Ball Z Kai

Son Goku is a skilled martial artist and a powerful warrior who at child lived so much adventures with his friends like Bulma, Master Roshi, Kuririn, Yamcha and Tien Shinhan, defeating some menaces as the evil Piccolo. Now, adult and father of the four years old son, Son Gohan, he lives a quiet and happy life with him and his wife and Gohan's mother, Chichi. But, during a friend reunion in Master Roshi's house (in a smaller island in the middle of the ocean), a stranger travels there introducing himself as Raditz and claiming that Goku is Kakarot, an extraterrestrial from the long time ago extinct planet Vegeta and a member of Saiyans, a humanoid race who lives killing another races and conquering their planets to sell them to the highest bidder later. Revealing that Goku was sent to conquer Earth just before the planet was destroyed, and realizing not only he failed in his mission to annihilate human race but he claims to be a hero and protector of planet Earth, Raditz kidnaps Gohan in an attempt to force Goku to fulfill his original mission. Will can Goku to defeat Raditz even when it would imply join forces with the own Piccolo?