In the midst of the 1960s, the affluent socialite Jennifer Stirling faces life-altering challenges following a devastating car accident that leaves her with significant memory loss. Struggling to recall her previous life and feeling a disconnect with her husband, Laurence Stirling, Jennifer stumbles upon a poignant letter hidden between initials "J" and "Boot". This discovery ignites her curiosity, compelling her to unravel the mystery behind the letter and her past.
Fast forward to modern-day London, where Ellie Haworth finds herself navigating the aftermath of a recent breakup and tasked with writing an article about her recently departed editor. In her quest for information, Ellie forges past the authoritative archivist Rory to explore the editor's records. Here, she stumbles upon an incorrectly filed romantic letter addressed to "J" from "Boot". The deep emotions conveyed in those words resonate with Ellie, instilling in her a determination to unveil the identities of the love-struck duo and the fate that befell their relationship.
Going back in time, a vibrant Jennifer and her husband Laurence enjoy a summer getaway on the picturesque French Riviera. It is here that they meet Anthony O'Hare, a foreign correspondent seeking to interview Laurence about his blooming business career. Nonetheless, their interactions are marred by Laurence's condescending demeanor toward both Jennifer and Anthony. Following a raucous party, a disheartened Anthony, having expressed his frustrations, catches Jennifer's attention.
The next day, Anthony presents Jennifer with a heartfelt written apology, which she insists he read aloud. He then extends an invitation for dinner, but plans change when Laurence must abruptly leave for a business commitment, leaving Jennifer and Anthony to share a summer brimming with budding emotions. They secretly begin an exchange of letters, donning their respective pseudonyms "J" and "Boot". As their connection deepens, an impulsive moment nearly brings them together, yet a sudden withdrawal leaves Jennifer shaken. Days later, an invitation from Anthony seeking a rendezvous at Postman's Park presents a turning point.
As their romance flourishes, Anthony proposes a daring escape to New York. However, Jennifer's fear of rejection from her social circle back home causes her to hesitate. After receiving a letter from Anthony stating he would await her arrival at the station, she is eager to restart her life with him. Tragically, a car accident strikes just before she can reunite with him, leading to significant memory loss, and Anthony departs, believing Jennifer has turned her back on their love.
Months down the line, Laurence is compelled to hide the last letter Jennifer had from Anthony, aiming to shield her from remembering the truth. Yet, Jennifer's spiral into confusion deepens as she unexpectedly discovers love letters from "Boot" tucked away in her home, along with an unopened postal box that Laurence had shut off. Confronting her husband, she learns from him that Anthony met his demise in the accident.
Fast forward four years, and fate reunites Jennifer with Anthony, rekindling her lost memories. Despite his pleas for her to leave Laurence, she grapples with her commitment as a mother to their young daughter. Deeply angered by Laurence’s lies, she asserts her intention to remain for the sake of their child yet promises to depart if he ever mistreats her. However, threatened by Laurence, who warns her of dire consequences, she grapples with her next move.
In the present, as Ellie and Rory delve deeper into the love letters, their bond grows stronger, even as Ellie hesitates after a passionate night together. Realizing that both Jennifer and Anthony are alive, she decides to confront them. Hearing their tales of love and lost opportunities catalyzes Ellie to embrace her own chance for love with Rory, rekindling her faith in romance.
In a bid to mend their broken past, Ellie encourages Anthony to compose one final letter to Jennifer, asking to meet once again at Postman's Park. From afar, she and Rory witness as the two star-crossed lovers are finally reunited, their hearts poised for a new beginning.
