In the wake of the tragic murder of Diana Floss in a Cape Ann, Massachusetts restaurant during 1972, her grief-stricken fiancé, Joe Nast, seeks refuge with her grieving parents. This marks the beginning of a poignant new chapter in his life. Ben Floss, Diana's father and a struggling realtor, attempts to cope with the loss of his business partner. Together with Joe, they embark on a venture to reinvent their original business plans, launching Floss & Son.
With a heavy heart, Joe retrieves their wedding invitations from the post office, only to be reminded of joyful memories by Bertie Knox, who helps him recover seventy-four out of seventy-five invites. Meanwhile, Ben tries to convince local developer Mike Mulcahey to back a redevelopment project aimed at invigorating a block of Cape Ann, but they face resistance from the tenants involved in the plan. Throughout this tumultuous time, Joe confronts bittersweet reminders of his love and engagement with Diana.
On a night out with Diana's friends at a local bar, the song "Moonlight Mile" sets a reflective backdrop for Joe as he interacts with Bertie. They share their sorrows, dancing under dim lights, where Joe confides in Ben about his struggles with grief, having ended his engagement just three days before Diana's tragic fate. Bertie, meanwhile, opens up about her boyfriend's deployment in Vietnam, forging a deeper bond as they navigate their individual losses together.
One night, Joe takes a risk by sneaking out to connect with Bertie. Their time together deepens their relationship, but upon returning at dawn, he finds Jojo waiting, her heart aching with the realization that Joe may never truly be hers. Tensions rise during a dinner with the Mulcaheys when Mike’s wife makes a casual reference to Joe’s lingering feelings for his late fiancée, prompting Joe to openly state that he has moved on. This causes ripples through the evening, ultimately resulting in the collapse of the business deal with Ben.
As unresolved feelings linger, Bertie challenges Joe about their ambiguous relationship. Their confrontation escalates when Joe expresses the community’s doubt about whether he would return to Diana, leaving Bertie emotionally unsettled as she departs. Meanwhile, the family finds themselves attending the trial of Diana's murderer, where grief weighs heavily upon them. A surprising display of emotion from the killer’s wife stirs sympathy among the jury, creating emotional chaos.
In a bid to counter this, prosecutor Mona Camp turns to Joe for his testimony, hoping he can shift the jury’s perception of Diana's life and untimely death. Taking the stand, Joe reveals the truth about their breakup, providing a vital piece of closure for Ben and Jojo, who finally understand they were not to blame for Diana's fate. This moment of clarity prompts Joe to write seventy-five symbolic letters, encapsulating his feelings and intentions. He shares these missives throughout the town in hopes of reaching Bertie and finding some semblance of peace.
As life begins to stabilize after this tumultuous chapter, Ben decides to close the family business, while Jojo reignites her writing career, channeling her heartache into her work. Bertie likewise opts to sell the bar, and eventually, she and Joe leave town together, marking the transition from a painful past into an unwritten future filled with new possibilities.
