Arthur Bach (Russell Brand) tries to attend an alcoholics anonymous (AA) meeting to straighten his life up for Naomi Quinn (Greta Gerwig) but he fails. Hobson (Helen Mirren), his trusty nanny, stands up for him and explains his situation as if it were her own. In the end they leave but the bond of nanny/mom and rich playboy is strengthened.
Hobson gets hospitalized while at Naomi’s place. Arthur straightens up to nurse Hobson back to health. While waking from a sleep at her bedside he finds her dead. So he drowns his sorry in a party until his wedding day to Susan Johnson (Jennifer Garner). Upon realizing it’s his wedding day he literally tries to drown himself in the tub. Bitterman (Luis Guzmán), his trusty chauffeur, gets him out of the tub and ready for the big day.
When the priests asks if there is anyone who objects, Arthur starts his speech about how he’s willing to give it all up instead of marrying Susan. Susan gets annoyed and punches Arthur in the face. Vivienne Bach (Geraldine James), Arthur’s mother, stands up for her son and allows him to leave with dignity. Arthur decides that he doesn’t want anything and starts taking his clothes off. He stops at his underwear as they were a gift from Hobson.
When Arthur exits the church he tells Bitterman that he is out of a job. Bitterman calls him a taxi and Vivienne gives him money for the taxi. She tells him that she respects him which is probably the closest she’ll ever to come to telling him she loves him.
Arthur finds Naomi’s place in Queens. Naomi rejects him and he wanders off. Next we find Arthur in an AA meeting with a 6 month sober chip. While walking around he sees Naomi’s book in a window display. Naomi has dedicated the book to Arthur. While purchasing the book he notices that Naomi is having a reading at the local library.
Arthur thanks Naomi for putting him out on the street to fend for himself. They leave hand in hand to find Bitterman in front of a row of movie cars. Arthur tells Naomi that his mother gave him his inheritance and he is silently running the Bach Charity organization. They ride off in the batmobile.