The film begins with Arthur (Russel Brand) and his butler Bitterman (Luis Guzman) dressed as Batman and Robin heading to Arthur’s mother’s fundraiser. They get involved in a chase with the police in the Batmobile because Arthur is very drunk. Arthur crashes the Batmobile on Wall Street and gets arrested by the cops.
At the fundraiser Arthur’s mother Vivienne (Geraldine James) and her business associate Susan (Jennifer Garner) are trying to keep investors happy by telling them that Arthur is bit more serious now. However, it is at this point that everyone gets the news about Arthur’s drunken arrest. The next morning, Arthur’s nanny Hobson (Helen Mirren) is cleaning up after Arthur’s party and interrupts Arthur as he’s having sex with a girl. Hobson erases all the pictures on her camera of Arthur’s shenanigans and takes away anything that she was trying to steal. Hobson tells Arthur that Vivienne would like to see him.
Hobson takes Arthur to Vivienne’s offices much to Arthur’s chagrin. Hobson assures him that he can watch cartoons afterwards. Arthur tries to avoid Susan on his way to Vivienne’s office but fails. They dates for 3 months but Arthur disappeared and broke up with her. Arthur awkwardly shakes Vivienne’s hand, demonstrating how alienated they are from each other. Arthur is the sole heir of Vivienne’s company and when he behaves the way he does, it frightens investors. As a solution, Vivienne tells Arthur that he has to marry Susan. The company has always been run by someone in their family and if she is part of the family, investors will be comforted. Arthur refuses and Vivienne tells him that he is cut off. Arthur wants to get married for love but in that case, he will lose 950 million dollar. Arthur relents and agrees to marry her.
After causing havoc at an auction house, Arthur wanders off and finds himself at Grand Central Station. He runs into a tour guide, Naomi (Greta Gerwig), who mistaking him for a bum, gives him some change after he asks where to get a drink. Arthur is attracted to her and follows her on her tour. She doesn’t have a tour license and is chased by a cop and Arthur follows suit chasing the cop chasing her. Once caught, Arthur tells the cops that it isn’t a tour but they are in fact their family. Arthur introduces himself as her fiancée and kisses her passionately in front of the cops. Once they placate the cops, Hobson drives up in the limo and tells him to get in. Naomi finds out exactly who Arthur is and excuses herself back to the tour. Arthur tries to ask her out but despite Hobson’s interference, Naomi gives him her number.
Arthur has a boxing match with Evander Holyfield while he gushes about his day with Naomi. Hobson punches Arthur out when he refuses to get ready for his 3:00 engagement proposal with Susan. Bitterman drops Arthur off at the under construction Burt Johnson tower to propose to Susan. He is left alone in one of the rooms with a nail gun and starts playing with it but is interrupted by Burt Johnson (Nick Nolte), Susan’s father. Arthur notices a telescope that is aimed directly at Arthur’s apartment across the way. Burt is convinced that Susan can turn Arthur around which is why he doesn’t mind that he will marry her. Burt has Arthur saw a piece of wood in half and then tries to get him to put his tongue through the saw. Once it detects the moisture of his tongue, it stops. After an awkward pause, he asks for his daughter’s hand in marriage.
At dinner that night, Arthur has dinner with Susan in which they discuss they’re apparent upcoming marriage and he tells her how it strange it is since they have absolutely nothing in common. Susan sees it as a business partnership and demands him to pull out the ring and say the words. After much stalling, Arthur reluctantly gets on one knee and proposes to her. Back home, Arthur laments to Hobson that his life is over and would rather be poor than marry Susan. Hobson has erased Naomi’s number from his phone.
Arthur tracks down Naomi on one of her tours. Arthur takes Naomi to Grand Central which he has completely rented out and emptied. There is just a circle of rose petals with a dinner table at the center of it. This is the fake first date that Arthur described to the cops when they first met. A fancy waiter comes out with a tray and takes off the cover to reveal Pez. Behind Arthur, there are acrobats. He says this is what money is for, for joy and happiness and acrobats. Arthur says they should go to Italy and when she asks when, he says tonight. Naomi requests that they should just be here. Naomi takes Arthur back to her home where they eat generic spaghetti-o’s. Naomi talks about her mother who died last year and Arthur talks about his dad who died when he was a child. Arthur finds a stack of drawings and stories that Naomi has drawn and written, which Naomi is very shy about. Arthur thinks its brilliant and that she should quit her job and concentrate all of her energy on a children’s book. Naomi says that’s not how the world works.
Arthur and Susan with their families take engagement photos where Arthur tells Vivienne that he has fallen in love with someone else but if he pursues those feelings, he will be impoverished. They try to take a picture of Arthur and Susan on a horse but Arthur is afraid of horses. Burt lifts him up on to the horse and Susan asks Arthur who the girl is. Susan gallops the horse away to have a private conversation. It is in the papers, Arthur’s date with Naomi. Arthur offers to cancel the wedding but Naomi refuses because she is not as rich as Arthur’s family. Arthur just doesn’t like her as a person. She is not spontaneous. Despite the warnings and the engagement, Arthur invites Naomi to his apartment. When he answers the door, instead of Susan, he finds Arthur standing at his doorway to his shock and dismay.
Susan arrives in a trenchcoat and underneath she is just in her lingerie. Arthur takes her to his bedroom and keeps her there when the doorbell rings. It’s Naomi. She is amazed by his apartment and Arthur tries to keep her away from his bedroom. Hobson offers to distract her while Arthur deals with Susan. Hobson takes Naomi to Arthur’s private movie theater where it shows only cartoons. Naomi offers Hobson to join her to watch. Back in the bedroom, Arthur tries to take care of Susan who is incredibly drunk.
Back in the theater, Hobson tries to figure out if Naomi is just after Arthur’s money. In the bedroom, Susan gets stuck under Arthur’s floating bed because she has metal on her and the bed has magnets on it. After Susan insults Hobson, Arthur leaves the bedroom and tells Hobson to detach Susan from underneath the bed while he goes out with Naomi. Arthur takes Naomi to a pond and they talk about a children’s book that they both have read that takes place around a similar looking pond. They kiss.
That night, Hobson reads that exact book to Arthur before he goes to sleep. Arthur tells Hobson that he is going to try to find a job in order to prove that he can live without the wealth. At an employment agency, Arthur finds he’s not qualified for anything but he gets assigned as a cashier at a toy store. Arthur takes a swig of liquor and the boss sends Arthur home and tells him to come back tomorrow and they’ll find something else for him in the store. They put Arthur in the stock room. Arthur gives the colorful mascot ten thousand dollars to wear his costume for one hour. The boss confronts Arthur and he falls down the stairs. Arthur is fired.
Arthur realizes that in order to get a job that he may have to actually be sober. Arthur wears a silly disguise and attends an AA meeting. Arthur gets depressed hearing the other people’s stories and almost leaves until Hobson gets up and says she’s an alcoholic. She then starts describing Arthur’s life to the AA meeting. After a long silence, Hobson and Arthur leave the meeting. Back in the limo, Arthur goes back to drinking but likes what Hobson said about him in there.
Arthur, drunker than usual, goes to Naomi’s house where he tells her everything about the engagement. Arthur tries to leave a check for a good deal of money to Naomi but she rejects it and kicks him out. Arthur begrudgingly goes back to Susan and toughs it out while Naomi works on creating her book. Hobson goes to see Vivienne and pleads Arthur’s case but Vivienne says that he is weak. Hobson says he’s stronger than he looks. Hobson goes to see Naomi and pleads for her not to give up on him. Arthur gets a call from Naomi. Hobson is in the hospital. She’s been having tests for months and apparently she is very sick.
Arthur talks to Naomi who is also at the hospital. She’s sold her book. She thanks Arthur for encouraging her writing and tells Arthur that he has a problem. Susan arrives and meets Naomi. Susan tells Naomi that the publishing company that bought her book is owned by Arthur’s company and was solely acquired to publish her book. Naomi, upset, leaves. Arthur catches up to her and she is upset that she didn’t earn it and that it was just given to her.
Back home, Arthur attempts to take care of Hobson by fixing her food and comes out with the generic spaghetti-o’s that he ate with Naomi. Arthur basically cares for her all day showing her favorite programs on the screening room and reading the newspaper with her and fixing her sandwiches. Hobson tells Arthur that he should call Naomi. She was in love once when he was three. She was going to go off to Spain with him but Arthur’s father died so she stayed. The next morning, Hobson dies.
Arthur is stuck in a depression now that Hobson is dead and throws a party. But he is still unhappy and is unmoved by the riotous party around him. Bitterman tries to cheer Arthur up but fails when he mentions that it is his wedding day. Arthur finds a note in his flask and asks a child to read it for him since he’s too drunk. It’s a note from Hobson telling him that he can do anything he wants to do.
At the altar, Arthur objects to the wedding. He claims it’s a sham wedding and claims that even she deserves better than him. Susan tries to threaten him to marry her so she can have his last name. Vivienne stands up for Arthur and asks him if he’s certain about giving up everything. Arthur says he is and is ready to start now and starts undressing. Arthur runs out of the church in his underwear and asks Bitterman to hail him a cab. Vivienne stops him outside and says he’s stronger than she thought. Vivienne pays for his cab ride and sends him on his way. Arthur runs through Queens and gets to Naomi’s house. Naomi says he should not have given up billions of dollars for her. She can’t be Hobson’s replacement.
Six months later, Arthur sits in an AA meeting and goes over all the mistakes and ridiculous stories of his wealthy days. None of the things he had could fill the hole inside him. He has been six months clean and has made amends with his mother. Passing by a bookstore, he sees Naomi’s book at the window and sees he was thanked on the inside cover. Arthur rushes to the New York Public Library where Naomi is doing a public reading of her book. Arthur tells a story to the kids after she’s done and tells a story of a prince who gives up his kingdom for a princess but had to give up “candy” first before they could have a relationship. He then apologizes to Naomi for hurting her and lying to her. They leave together and they’re going to try to make it work. Arthur tells Naomi that his mother did in fact give him his inheritance and he has been secretly running the Back Charity organization.
It is assumed they end up together and live happily ever after.
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