Cassie Salazar, played by Sofia Carson, works as a waitress and bartender while pursuing her passion for music with her band, The Loyal, alongside Nora (Kat Cunning), at a local bar. After being diagnosed with Type 1 diabetes just six months prior, she faces numerous challenges in affording insulin and sustains herself through multiple jobs. One fateful evening, she encounters a group of Marines about to be deployed to Iraq. Among them is Luke Morrow, portrayed by Nicholas Galitzine, who attempts to flirt with Cassie, but she declines his advances.
Luke carries his own burdens; he fell into addiction following his mother's death and is trying to navigate life as a recovering addict, yet he still owes a hefty $15,000 to his dealer, Johnno, played by Anthony Ippolito. Complicating matters, Luke is estranged from his father, Jacob Morrow Sr., portrayed by Linden Ashby, and reaches out to his brother, Jacob Morrow Jr., played by Scott Deckert, only to be turned away.
In a desperate attempt to solve their financial woes, Cassie proposes a marriage of convenience to her childhood friend Frankie, played by Chosen Jacobs, who is also Luke's bunk-mate. Though Frankie hopes to marry his true love, Riley, he considers Cassie's proposition. Luke, overhearing their conversation, warns against the idea of a fraudulent marriage, but soon realizes that both he and Cassie could benefit immensely from such an arrangement. They finalize their plan to wed before Luke's deployment, planning to divorce after a year.
With Frankie as their witness, Cassie receives a sentimental gesture when he gives her the ring he intended for Riley, asking her to keep it safe. Later, they celebrate their nuptials with Frankie and Luke's fellow Marines, leading to a heated exchange between Cassie and Armando, played by Nicholas Duvernay, over a distasteful toast. Afterward, she comforts Luke, who admits his fears about the war and their marriage, leading to an intimate night they share together.
As the Marines head off for deployment, Luke provides Cassie with his brother’s contact details, marking her as his next of kin. They maintain their ruse through emails and video calls, giving rise to a beautiful song Cassie writes titled "Come Back Home," which eventually goes viral. When Luke inquires whether he serves as her muse, Cassie acknowledges it might be the case.
Tragically, during one of her performances, Cassie receives distressing news: Luke has been gravely injured by an IED blast and is returning home. An unfortunate mix-up causes her to contact Luke's father instead of his brother, escalating tensions as Luke's father, a retired Marine officer, could expose their fraudulent marriage. As their lives intertwine further, Cassie learns of Frankie's death in action, prompting her to pass his ring onto Riley at his funeral.
Upon returning home in a wheelchair after his hospitalization, Luke moves into Cassie’s apartment, crafting a wedding ring for her from his dog tag chain. They work together to revamp their living space, preparing for visits from Luke’s father, who comes to assist with therapy. To help Luke heal emotionally, Cassie adopts Peaches, a golden retriever, as an emotional support animal. Inspired by their journey, Cassie writes another heartfelt track, "I Hate the Way," which she delivers passionately at Whisky a GoGo, catching the keen interest of record labels.
However, as unpaid debts loom over Luke, Johnno threatens Cassie's mother, Marisol, played by Loren Escandon, leading to an intense conflict. After a worrying health scare for Cassie, where her sugar levels drop and she nearly loses consciousness, Luke steps in to help. A subsequent confrontation with Johnno results in Luke physically defending his wife and attempting to settle their dangerous debt.
Eventually, after an emotional confrontation regarding his past misdeeds, Cassie decides to divorce Luke, setting a deadline for him to vacate her apartment. Things take a turn when Luke is apprehended by the MPs due to Johnno reporting their fraudulent marriage. At the trial, Luke chooses to plead guilty, shouldering the blame and asserting that Cassie had no knowledge of the violations. He is sentenced to six months in the brig, followed by a Bad Conduct Discharge.
As Cassie's band secures a record deal and prepares for a major performance opening for Florence and the Machine at the Hollywood Bowl, she unveils a new song inspired by Luke titled "I Didn't Know," a moving piece written while she awaited his trial. Rushing to share her love for him before his departure, Luke gives Cassie his wedding ring, affirming that "it's real now."
The film culminates in a heartwarming scene six months later, where Cassie and Luke enjoy a blissful picnic at the beach alongside Peaches, embracing their love and the life they’ve built together.
