Fletcher (Jim Carrey) is a well-known lawyer. In order to win the lawsuit, he has developed a skill of reversing right and wrong and black and white, that is, telling lies. Lying has become Fletcher's instinctive reaction, even when facing his wife and 5-year-old son Max (Justin Cooper). His wife and children have long been accustomed to his style. This day is Max's birthday, and Fletcher can't come because of something. Fletcher naturally lies and makes up all kinds of excuses. Fletcher, disappointed, made his birthday wish: his father can't lie one day. A magical thing happened! Fletcher really can't lie anymore, and he is in a mess: he almost lost the lawsuit, offended his boss... How will Fletcher, who is in unprecedented chaos, face all this?