Arulco Liberation is the main quest of Back in Action. Completing this quest requires killing Queen Deidranna, who's in her heavily guarded Palace near Meduna. She is normally in the back of the palace, in the room next to the helicopter. Note: killing Deidranna and thus completing this quest finishes the game, so if you want to complete other quests or just play around in Arulco, you will have to delay killing her.