Raditz had taken Gohan hostage and when you and Goku were about to follow him Piccolo arrived and offered to team up. The only reason he was wanting to team up is because Raditz is getting in his way of world domination, despite this Goku agreed to team up to save his son

While you, Goku and Piccolo were fighting the Saiyan, you and Piccolo were knocked back and now found yourselves in a valley, you're not sure which way you came from