Arthur (played by Russell Brand), the rich Buck family heir, is a well-known Peter Pan-style figure in New York City. His absurd behaviors such as disguising as Batman are repeatedly reported, which makes his mother in charge of the family company feel very stressed.Arthur's behavior like an ignorant child often requires the old housekeeper Hobson (Helen Mirren) to clean up the mess. His mother could not bear Arthur's behavior of discrediting the company's reputation, so as to cut off his source of income to threaten Arthur to marry his capable female assistant Susan. Susan has career ambitions and is determined to rely on this marriage to enhance her status as a builder's family.Arthur, who saw his mother bowing his head for money, met Naomi (Greta Gerwig), an unlicensed tour guide on the street. His style made Arthur love. At the fork between marriage and love, Arthur hoped to find a perfect ending, which may be the strongest challenge he faced in his life.