When a daring mission leads a deep sea submarine team into a mysterious opening on the ocean floor, they uncover a lost underwater world and awaken its ancient race of otherworldly beings. 前一阵子销声匿迹的女魔头天魔再次出山，这次她的目的是印在乌龙院里面壁大师右手掌舵洗髓经。于是，天魔收买了糊涂杀手黄柠檬（张卫健 饰）和红柠檬（叶全真 饰），派两人前往乌龙院砍下面壁大师的右手掌带回来。 
