Adaline Bowman, a young woman born in the early 20th century, experiences a miraculous occurrence in the 1930s that renders her ageless, perpetually appearing to be 29 years old. Heartbroken by the death of her husband and aware of the implications of her condition, she leads a solitary life for over eight decades, relocating and assuming new identities to conceal her secret. Adaline's only constant is her daughter, Flemming, who ages normally. Against her better judgment, she starts a romance with a charismatic man named Ellis Jones, challenging her resolve to remain detached from emotional entanglement.

As Adaline grapples with this new relationship, a chance encounter with Ellis’s father, William, dredges up memories from her past that threaten to unravel her carefully guarded secret. This twist of fate forces Adaline to confront the life she has been running from and the decisions she must make about her future. She must choose whether to continue her existence of isolation or embrace the possibilities of love and connection, even at the risk of exposing her true nature.