教师阿志（郑伊健 饰）自小怕水，一次溺水被人鱼小美（钟丽缇 饰）所救，小美体内的珍珠却被阿志误吞下肚。失去了珍珠的小美无法回到大海，只好假扮学生进入了阿志所在的学校，希望拿回珍珠。没想到阿志得知秘密后就算被吓坏了，还是依然与小美展开了一段唯美的人鱼恋。纸包不住火，小美的秘密最后让校长（郑则士 饰）知道了，校长决定抓住小美。虽然阿志极力救出阿美，他们的恋情却又遭到了挑战。After falling in the water and almost drowning, a young schoolteacher finds himself lying on a beach, unable to remember what happened. Unbeknownst to him, his rescuer is a mermaid, who has fallen in love with him. To pursue her love, the mermaid comes onto land and enrolls in his school as a student. Things don't work out as she planned, however, as she soon attracts the jealousy of the other girls in the school. To make matters worse, she must hide her secret from a gang of fortune hunters who would like nothing better than to catch their very own mermaid.