The plot follows two main storylines: one centres on the emerging love story between two awkward teens, Jens and Lisa, who are having sex for the first time; the second focuses on the eventful quest of Simon the Semen and his friends to reach the golden goal, the Egg.

外星巨兽“屁屁怪”突袭地球，引发大规模破坏，全球迅速进入一级戒备状态。一时无策的军方决定向全球公开征集顶尖的机器人设计，以对抗这场危机。热爱发明的麦兜（张正中配音）带着自己研发的“电饭宝”加入比赛，意外之下竟然成功入选。从这一刻起，拯救地球的希望全都寄托在麦兜身上！但麦兜是否能肩负使命，成为足以拯救地球的英雄呢？