A woman given the birth name Adaline Bowman and her current alias, Jennifer Larson, was observed buying phony identification at a San Francisco flat. She could have shaved off a few years, so the forger asks her why she opted to be 29 given her appearance. He's too kind, she replies with a smile. She questions why he fabricates IDs when he is capable of much more as she leaves. She adds that the autographed baseballs on his desk reveal his true name. "You make mistakes with the little things," she explains.
When Adaline returns to her flat, her dog welcomes her. She has raised the same dog repeatedly in her 107 years of life. She says she needs to arrive on time for work at the archives office of the library. There, Adaline Bowman opens a box containing film reels that depict historical events. She was the first child born in San Francisco on New Year's Day, 1908. She had married in 1929 and had a daughter, Flemming, in 1932. In 1937, she lost her husband in an accident while the Golden Gate Bridge was being built, leaving her widowed. One night, while she is heading to her parents' house, an inexplicable snowfall starts. Unfortunately, she met with an accident and fell into a ravine, a cold lake in Sonoma County. Adaline was struck by lightning and resurrected, but since then, Adaline has never grown older than 29. It is hardly evident at first, but as her daughter gets older, it becomes more noticeable.
She gets pulled over one day by a police officer, who takes away her ID because it indicates she is 45 years old. She flees and lives on the run for the remainder of her days. After a year of research at a medical institution, she decides to move away and finds no explanation for her illness, which prevents her from aging.
In 1953, she was walking home late one rainy night and was followed by two FBI agents. They try to transport her to an airplane after putting her in a car for research purposes. After breaking free from the trunk, she explains this to her adult daughter, and they say their final goodbyes with great emotion. She decides to live a life of evasion, adopting a new appearance and persona every ten years.
She walks into the hotel on New Year's Eve to find a party going on. There's a photo of her with friends on the wall, and it's obviously from many years ago. She looks at it in silence before going to find her buddy, who is hosting a party and playing the piano. Adaline's friend, who is blind, makes fun of them both by calling them cougars because they only pursue young men (her buddy thinks they're both old ladies). Adaline instantly pins a young man who approaches her in a Sherlock Holmes-esque manner.
She can tell he's an artist from an affluent background by the paint on his hands and the pricey heirloom watch he's wearing. Ellis Jones enters the room as they are chit-chatting. Adaline glances away as the brunette gives Ellis a cheek kiss after they exchange a glance. She exits the room at midnight and gives her daughter a call. Her daughter confirms lunch the following day and sings Happy Birthday over the phone. Adaline is approached by a young man who tries to pull off a convincing prank about kissing a stranger at midnight. She responds that she has heard it before, from a young Bing Crosby-type, when he asks if she has. After bidding her companion farewell, she makes her way to the lift.
Ellis opens the lift with a push of his hand, allowing them to descend together before it closes. He tries and fails to soft-talk her. She also confirms that the girl kissing him on the cheek was not Ellis’s date. She declines him courteously and walks to her taxi. There's a moment with her daughter where she mentions that she wants to move to an Arizona retirement community and that she has difficulty climbing stairs. Angry, Adaline states she was going to go to Oregon to spend more time with each other.
Her coworkers at work the following day note that a kind donor is scheduled to drop off some books. Whoa, it's Ellis! Surprise! He delivers her books with flowery titles (a reference to their lift chat). He must have seen her at a board meeting previously and known she was employed there. She promptly declines his invitation to participate in the publicity shot they are taking because she dislikes being photographed. She declines his offer of a date when he makes one. Then, if she says no to the date, he threatens to retract his donation. Reconsidering that, she accepts a date to go for it.
They are in the tunnels under San Francisco in the next scene. A boat was discovered. He fills her in on a lot of personal details before inquiring about her. She won't say much more than, "I have a dog." He offers to tell her a joke as they walk away, and if she laughs, she has to go out with him again. She chuckles at a stupid joke he tells. Adaline gets a flashback to when she first started the account and adds a co-signer to her account in the present (her new identity). Her financial condition can be explained by her successful investment in Xerox. She intends to move soon to live on an Oregon farm.
Adaline returns to Ellis' flat for their next date, where they enjoy wine, hot dogs, and jazz music. Ellis is a philanthropist, and his friend is currently in Fiji. He found an algorithm while majoring in mathematics. Ellis's friend made money off of it, so they divided the earnings. Together, they slept through the night. Ellis is on the phone the following morning, struggling to understand a work call that is in Portuguese.
Adaline quickly texts someone in Portuguese on his phone and walks away. Adaline also sees an unidentified man in a flashback. He's tinkering with the ring for his engagement. She declines to see him. She answers none of Ellis's calls, presumably as a result of this memory. She moved to Chinatown, Timbuktu, and she has had to put her dog down during this period. While going through old photos, it's obvious how lonely she is. When Ellis arrives at her budget flat in Timbuktu, she becomes frightened and demands to know how he discovered her address. She dismisses him. She experiences a change of heart.
Adaline, who meets his daughter, tells her that she is tired of running all these years. Flemming tells her to quit running because the individuals who were hoping to apprehend her have long since passed away. Adaline also mentions Ellis, whom she recently met. Flemming suggests going after him, at least for her. Listening to Flemming, Adaline comes back to Oregon. She returns to Ellis's desk to offer her apology. They take a date to an antiquated drive-in theatre with a canopy. She gives a history lesson as though she were present, which she was. While sipping wine, they gaze up at the ceiling's stars. She agrees when he invites her to his parents' 40th anniversary celebration.
She picks up his sister and drives (jokingly) as if she has nine lives on the way there. As soon as they go inside his house, William Jones, Ellis’s father, greets and recognizes her right away and calls her Adaline, even though she goes by another name. She claims that her mother, Adaline, died away some time ago. They were quite close, he says, shaking with shock. Another flashback shows how they came to be together. Adaline was living in England, and Williams studied medicine abroad as a soldier. One day she was experiencing car problems. Williams was the man who helped her, and from then on, they spent their time together for the next 5 weeks. Adaline made the mistake of revealing her actual name and her moniker, ‘Della’. Three weeks later, she completed her semester, and William flew home to the United States. Adaline came with him.
The following morning, William answers his wife's question about how he met Jennifer’s mom. He explains that they were together, and they left for America. William says that he was frightened that he would run out of time, so she encouraged him to pursue his ambition of studying astronomy rather than medicine. He explains characteristics of Adaline that Ellis notices, like her aptitude for driving and interest in other languages. William's wife gets a little irritated when he talks endlessly about Adaline.
They played trivia that evening. William has won 47 straight games. Adaline acts as though she has no idea, but after Ellis gives her a hard time, she gives it her all and prevails. The family makes jokes about “what would happen first—Williams's trivia loss or Della's arrival?” Della, the name he gave the meteor, said it would arrive but didn't. His family thinks that he named Della after his aunt Adele, but actually, he named her after Adaline. Knowing that Jenny gets shocked. When Jennifer asks William why he named that comet after her mother Adaline (i.e., Della), William replies, “If my calculations were correct, which turned out to be wrong, it would’ve been the closest approach to Earth of any comet in 200 years. In other words, like your mother, a near miss. I was going to propose to her. I had an engagement ring in my pocket. She stood me up. Near miss”. William was the man with the engagement ring, as shown by a flashback. At present Adaline says, "She loved you too.” The same night, Ellis confesses his love to her.
On the day of the celebration, everyone is out and about. During their conversation, William observes the scar on her left hand from stitches he made during their hike; however, it isn't revealed how her scar doesn't heal, how her hair grows, or any other specifics if she is eternal. (Yes, the same scar.) He searches an old shed for a picture to confirm that he is not hallucinating. He discovers the scar, which turns out to be from a cut she had decades earlier while trekking with William, and he is horrified. When he approaches her, she affirms who she is and says she has no idea what has changed. William asked her if this was the reason she left him. Yes, she responds. Despite William's pleas for her to stay for Ellis's sake and not to run, Adaline sprints towards the house quickly writes a message to Ellis, packs, takes his car keys, and departs.
Ellis approaches his father after seeing the letter, but he won't talk. Ellis is still pleased with what has happened, and William replies that “she is not capable of change.” Adaline refuses to pick up his calls. William asks Ellis how he knows that he loves her. Ellis confronts William, saying that nothing makes sense without her, William asks Ellis to go after her. When she stops, Adaline is driving through the woods. Adaline thinks back on all the times she has run while driving home. She informs her daughter over the phone that she is giving up running. A tow truck smashes into her as she turns the car around and takes off. After being thrown from the automobile, Adaline succumbs to hypothermia. Suddenly, snow starts to fall again. When Ellis arrives, he observes the situation. After a defibrillator is used by the ambulance crew to revive her, Ellis is by her side when she awakens in the hospital.
When she wakes up, she chooses to tell Ellis the truth. Adaline shares her 107 years of life and her fear of being found out as they declare their love for one another. Once she sees Ellis, her daughter says, "I'm her grandmother." When Adaline tells her he knows, she hugs him and sobs with happiness.
Ellis and Adaline are attending a New Year's Eve celebration a year later. Although Adaline has a date night at home (with another puppy), she encourages her daughter to go out. Adaline gives herself a second look in the mirror before heading out. Grey hair, a symbol of aging, is plucked by her. She tells Ellis that she's fine and that she's great. It seems that her hypothermia and defibrillators have brought her back to humanity. And here comes Della, the meteor. Though it's fifty years too late, it's more relevant than ever.
