Former pro golfer Wallace Avery (Colin Firth) is struggling with boredom, depression, and a life from which he longs to escape. Trapped in an unfulfilling FedEx floor manager job in Florida, he finds little comfort in his failed first marriage or his current relationship with his girlfriend Mina (Anne Heche). He has even become estranged from his teenage son Kevin (Lucas Hedges) who has come to resent him. Driven to desperate measures, Wallace decides that he needs a new start and a new life.
Faking his own death by drowning on a deserted beach, he acquires a forged passport and a new identity—that of a golf pro named “Arthur Newman”. Leaving Florida behind, “Arthur” heads out for Terre Haute, Indiana to start a new life and a new job as a resident golf pro at a club. Along the way, he meets a beautiful but troubled young thief. He takes her to the hospital after finding her slumped beside his motel swimming pool from a near-lethal dose of morphine-infused cough syrup. The young woman, Charlotte Fitzgerald (Emily Blunt), is also traveling under a false identity—that of her paranoid-schizophrenic twin sister, Michaela or “Mike”—and has fled her home in Durham, North Carolina.
Arthur and Mike become traveling companions and eventual lovers on their way to Indiana. Mike thinks up a game in which they spot interesting-looking couples, break into their homes, dress up in their clothes and pretend to be them. Unbeknownst to Arthur, Mike collects souvenirs/prize possessions after each game. Meantime, Wallace’s teenage son Kevin initiates an unlikely friendship with his father’s former girlfriend Mina. Together they struggle to understand the man who skipped out of their lives.
At this point of time, both Mike and Arthur have only been physically intimate as the identities they have undertaken throughout their travels together. It is very apparent that Arthur has very quickly fallen in love with Mike before she reciprocates. Despite being physically intimate with each other’s assumed identities, Mike and Arthur continues to sleep in separate beds, but they carried out highly personal conversations as their true self—Charlotte and Wallace.
Before Arthur and Mike reach Terre Haute, Indiana, Arthur asks Mike to stay in Terre Haute with him as they live their new lives (Michaela – Arthur) together. Mike seemed distress over Arthur’s proposal. It was later revealed that Charlotte was afraid of ending up like her sister and mother who are both paranoid-schizophrenic. She cried out, “How can I live with anyone? I am a genetic time bomb.” Arthur then comforted her, “You’re not a statistic Mike, you’re a person. Can’t defend yourself against your worst feelings. You feel the things most of us run away from, most of us just too bummed out to feel”. They held hands and Mike cried out, “Now do I have to have sex with you? Because I really don’t want to.” Arthur laughs, responded while shaking his head,” It’s okay.” They held hands as they fell asleep together beside the pool that night.
Later on, both Mike and Arthur dressed up as they reached Terre Haute Country Club to meet the Chuck Willoughby—the boss of the golf course who promised Arthur a job which gave him the epiphany to desert his old life behind. As they missed Chuck at his office, they decided to head for dinner. Mike and Arthur were extremely flirtatious and their conversations began to take a turn when Mike joked about Arthur being childless, another lie Wallace made up. Wallace begins to be angry as his manhood was questioned and he left the restaurant with Mike following behind. Coincidentally, they met Chuck and his friends. Chuck began praising Arthur’s golf skills and flipped the table around by calling him out for his lies. After verification online, Chuck realized there is no golf-pro called “Arthur Newman”. He threatens to call the cop on Arthur and his whore—Mike (Mike self-introduced herself as Arthur’s whore). However, Chuck decided to laugh it off and walked away with his friends. The issue of his child and his dream of a new life gone, Arthur was disappointed and frustrated. Arthur and Mike return to their motel room, back to their separate beds. Arthur began saying that Mike was just putting an act, a facade to escape what has actually happened which angered Mike.
The next morning, Arthur woke up, Mike-less. He went straight to his drawers and realized his money was gone. He decided not to vacate the room because he has nothing to look forward to. He then hung a “Do Not Disturb” sign on the door. Arthur was then met with a knock on the door, inviting him down to the police station because Mike was caught. Arthur then discovered Mike’s souvenirs/prize possessions and defended her by saying he gave her the 29,000 dollars, instead of her stealing from him. Mike was then released from the station as Arthur did not press charges. As Mike saw Arthur, her first response was, “I am not gonna try to justify what I’ve did”. Which Arthur too shared similar sentiments. They began recounting the John Doe who convulsed and died at the bus station where Arthur first tried to send Mike away. Arthur handed John Doe’s wallet to Mike, revealing his name was Beauregard Tully, who lived in Newport News, Virginia, drove a truck to Walmart, diabetic, went to Alcoholic Anonymous (AA), had 2 kids (John and Matt), had a Wife, Rosita and they were married for 23 years. Arthur and Mike drove down to visit Rosita to reveal the sad news and to return Beauregard’s belongings.
Eventually, the role-playing games that Arthur and Mike have engaged in lose their appeal, revealing two hearts that have been hurt by life’s challenges. The two are forced to take another look at themselves and the lives they’ve left behind. Arthur decided to return home to reconnect with his son, and decided that Mike needs to return to her sister. After Mike thought things through, she decided to return to the room and finally, they love each other as themselves. The morning after, Wallace drives Charlotte to her hometown of Durham, so she can look after her schizophrenic twin sister—Mike. As he prepares to leave, they kissed and he assures her that he knows where he can find her. Wallace then drives back to his hometown in Florida to reconnect with his son.