The film unfolds in Seattle, showcasing an aging golden retriever, Enzo, who’s lying in front of a door. Although he’s alive and aware, his movements are minimal. As we dive into his thoughts, Enzo reflects on nearing the end of his life while reminiscing about a fascinating belief he encountered on television — that Mongolians feel that dogs are reincarnated and eventually return as humans after living a complete life. He perceives his inability to communicate with humans as a curse, all while he anticipates the arrival of his devoted owner, Denny.

When Denny returns home, he discovers Enzo nearly immobile and soaked in his own urine. The grim reality dawns on Denny — he knows their time together is running short. He gently lifts Enzo, placing him on the couch, where the golden retriever begins to share their intertwined story.

Initially, we see Enzo as a puppy boxed with his littermates, fully aware that he is unique. His life changes when Denny comes along; their bond forms as Enzo rushes over to lick Denny. After some playful negotiations, Denny decides to adopt him. The duo quickly settles into their lives, with Denny introducing Enzo to his friends and responsibilities as he juggles a teaching job in auto racing and dreams of being a professional racer. Gary Cole, as Denny’s boss Don Kitch, supports Denny’s aspirations, recognizing his talent.

Time progresses, and Denny meets Eve, played by Amanda Seyfried, while grocery shopping. Enzo senses Denny’s budding affection for Eve and reacts jealously, attempting to obstruct their connection. Despite this, Denny invites Eve to a friend’s concert, where they spark a romance that blossoms into marriage. Yet, tensions arise with Eve’s disapproving parents, also referred to humorously by Enzo as the “twins,” who disapprove of Denny’s racing lifestyle.

As Eve becomes pregnant, Enzo feels a shift in the household. He grows fond of her, sharing intimate moments, like resting his head on her belly and feeling their baby, Zoe, kick. However, Denny’s determination to compete in a pivotal race leads him to leave for Daytona, believing Eve will manage just fine during her pregnancy.

Eve gives birth while Denny is racing, and when he returns home, he finds a beautiful but complex family dynamic emerging. Unfortunately, challenges await as Eve begins to suffer from severe headaches, leading to the painful discovery of her illness, which Enzo can sense but cannot articulate.

As Denny navigates the struggles of juggling races, family time, and Eve’s deteriorating health, tensions rise. During a thunderstorm, Enzo finds himself feeling frantic, hallucinating odd scenes while being left alone by a sick Eve. After Eve’s health takes a turn for the worse and she enters the hospital, Denny struggles to care for Zoe while enfolding Enzo in his love.

The narrative takes a heart-wrenching twist when Eve eventually succumbs to her illness. The aftermath brings about a confrontation with her parents, who seek custody of Zoe, pulling Denny deeper into a legal struggle that leaves him grappling for answers. Denny is falsely accused, leading to an arrest that further jeopardizes his custody battle.

As fate would have it, Denny is given an opportunity to work in Italy, testing for Ferrari, but feelings of despair and doubts loom large. Enzo, now older and feeling the weight of time, encourages Denny to fight for his daughter and reject an unfavorable custody deal.

In a dramatic court scene, the truth surfaces, leading to Denny securing custody of Zoe, finally allowing him and Enzo a moment of hope. The film elegantly circles back to its opening, highlighting Enzo’s reflections on his life and the love shared with Denny and Zoe. With newfound resolution, they embark on a journey to Italy, setting the stage for a new chapter in their lives.

Years pass, and we see Denny in racing gear, now a successful Formula One driver. An encounter with a young boy named Enzo sparks memories of his beloved pet, promising to carry the legacy of their shared journey into the next phase of life. As Enzo prepares for rebirth, he believes he will finally embrace being human, filled with the lessons learned from a life filled with love and adventure.