As Wallace Avery (played by Colin Firth) grapples with a life filled with monotony and despair, the burden of his depression intensifies, suffocating any glimmer of hope. Once a professional golfer, he now finds himself ensnared in a lifeless FedEx job in Florida, grappling with the aftermath of a failed first marriage and an unsatisfying relationship with his girlfriend, Mina. These aspects serve as constant reminders of his stagnant existence, compounded by the emotional distance from his teenage son, Kevin. In a moment of desperation, Wallace hatches a bold plan to reinvent himself.
He assumes the identity of "Arthur Newman," fabricating a new persona complete with a false passport and a fresh start. With aspirations to leave his past behind, he sets off for Terre Haute, Indiana, aiming to reclaim his identity as a golf pro at a local country club. On his journey, he encounters Charlotte Fitzgerald (played by Emily Blunt), a young woman with a troubled past and a hidden agenda. Charlotte cleverly navigates under the guise of her twin sister, Michaela (known as Mike), who struggles with paranoid schizophrenia.
As Arthur and Mike embark on their escapade toward Indiana, they form an unexpected alliance. Mike introduces Arthur to a peculiar game in which they impersonate interesting couples, infiltrating their homes to don their attire. However, unbeknownst to Arthur, Mike has a penchant for collecting mementos from each home they visit. Back in Florida, Kevin finds solace in an unlikely friendship with Mina, both of them trying to come to terms with the absence of the man who left them behind.
As their journey unfolds, Arthur's feelings for Mike evolve. Despite the complexity of their dual identities, their emotional connection deepens, largely revealed through their candid conversations as Charlotte and Wallace. It becomes evident that Arthur is irresistibly drawn to Mike. Nevertheless, the shadows of her insecurities create tension between them.
Before reaching Terre Haute, Arthur proposes a future together, only for Mike to voice her profound fears of potentially succumbing to the same fate as her mother and sister, both plagued by paranoid schizophrenia. Guided by compassion, Arthur acknowledges the weight of her concerns.
Upon arriving at the Terre Haute Country Club, Chuck Willoughby, the owner, becomes suspicious of Arthur's fabricated golf persona after praising his supposed skills. Just as Chuck threatens to notify the authorities, he can't help but laugh off the charade, leaving Mike and Arthur at a crossroads, contemplating their next steps.
The following morning brings a harsh reality: Arthur awakens to find Mike gone and their shared funds missing. Instead of fleeing the scene, Arthur, burdened by a sense of emptiness, opts to stay behind. His decision leads to an unexpected summons to the police station, where officers inform him that Mike has been apprehended. Shockingly, Mike has confessed to stealing Arthur's money, and he's prompted to decide whether to file charges. In an unexpected twist, Arthur crafts a lie, insisting he willingly gave Mike the money, revealing his affection for her. The officers, however, disclose that Mike is a kleptomaniac, showcasing stolen items, including the wallet belonging to Beauregard Tully.
Arthur's heart drops as he recognizes the photograph inside the wallet of the man he attempted to save at the bus station, where Mike stayed by his side as he passed. He could easily have chosen to walk away from Mike, but instead, Arthur decides to bail her out, concealing Beauregard's wallet in his pocket. Released into Arthur's care, Mike steps back into his life.
As they leave the station, the unique pair reflects on the John Doe whose life had ended where their paths first crossed. Their journey continues to Virginia with the intent of returning Beauregard's belongings to his wife, Rosita, and their two sons. Along the way, they indulge in whimsical role-playing games as a way to escape the burdens of their tumultuous lives. Yet, as they confront their own challenges, Arthur resolves to return home to reconnect with Kevin, while Mike realizes the importance of reuniting with her sister.
The next day, Wallace sets off to drive Charlotte back to her hometown, where she can care for her ill twin sister. He assures her that he knows exactly where to find her and embarks on the journey to mend his relationship with Kevin. In a bittersweet conclusion, Charlotte reunites with the true Michaela, while Wallace stands at his son's doorstep, signaling the hopeful beginning of a new chapter for both of them.
