When Jacob Jankowski,parents dead and suddenly adrift, jumps onto a passing train, he enters a world of freaks, drifters, and misfits, a second-rate circus struggling to survive during the Great Depression, making one-night stands in town after endless town. A veterinary student who almost earned his degree, Jacob is put in charge of caring for the circus menagerie. It is there that he meets Marlena, the beautiful young star of the equestrian act, who is married to August, the charismatic but twisted circus owner. He also meets Rosie, an elephant who seems untrainable until he discovers a way to reach her.
The movie begins with an elderly man (who is actually Jacob - Hal Holbrook) outside after a circus performance, looking for his ride, when younger workers notice him and ask if he is lost or needs to go back to the home. He insists that he doesn't belong in a home and becomes quite upset when they persistently ask, but then apologizes for his rude behavior. The young men bring him inside from the rain, and while one man goes about calling the old folks home, the other notices Jacob looking at the pictures hanging on the wall. The young man is shocked to find out Jacob knew about the circus and even more impressed when he says he was there, right in the middle of it. It is explained that it was the most famous circus disaster in history. The young man passes him an old photograph of a young woman sitting on an elephant's trunk, and Jacob tears up. The young man asks Jacob to tell him what happened in 1931, and so the story begins.
The movie flashes back to 1931, as a young man (younger Jacob - Robert Pattinson) was preparing to take his final exam at vet school. He lived at home with his parents who had left Poland to seek a better life in America. The police show up during his exam to break the news that his father and mother were killed in a car accident. After identifying the bodies, he ends up throwing up in an alley.
The news gets worse when it is explained to him that the bank is taking all his family's assets due to his father's defaulting on loans. The young man insists that his father was a good man, and the family home was paid for. He shortly realizes that his parents had mortgaged their home to send him to vet school. Jacob leaves his boyhood home with one suitcase and plans to walk to Albany where there would be jobs, but he didn't make it to Albany. He hops on a passing train and meets some older men, who offer to help him find work the next day.
They arrive at an open field, where a large group of men file out of the train and begin constructing the circus tent. Jacob is in awe of the entire process, but is soon thrust into shoveling manure. While working, a pretty woman catches his eye (Marlena - Reese Witherspoon) as she is talking to horses, asking one if it's okay. It is pretty clear she is part of the act and Jacob walks over to take a look at the horse's leg. She quickly turns away from him, taking the horses with her. Jacob follows her and witnesses with amazement her circus act with the horses. He asks one of his fellow workers about her and is told she is the boss's wife and you don't talk to her.
Jacob is introduced to the August (the boss) and impresses him enough to become the new veterinarian. He is then introduced to Marlena and she, once again, brushes him off. He examines one of the horse's injuries and explains to August that he should be put down. August tells him that is unacceptable and to make it work so the horse can perform through the season. He stumbles upon Marlena, who is comforting the injured horse and they have a short conversation about how the horse should be put down. Jacob grabs a gun, but before pulling the trigger, Marlena tells him it will be his last decision if he goes against what August says. He pulls the trigger and Marlena tells him she will be sad to see him go. August finds Jacob and threatens to throw him off the train.
To help fill the money void left when the star horse was put down, August buys an elephant named Rosie and insists that, with Marlena in the mix, he will sell out crowds. It is quickly established that Marlena both appreciates and adores the way that Jacobs cares for animals and they bond over training the elephant. Later, Jacob is invited to drinks with August and Marlena to celebrate the addition of Rosie to the circus. During drinks, August states that he wants Jacob to be the Bull Man, and Jacob explains he is not a real vet, as he did not receive a degree. August shockingly doesn't mind and they drink a cheer to Rosie. After an awkward moment with August, who is very drunk, Marlena puts him to bed. Jacob asks if he should go, and Marlena tells him to dance with her just once and then he can go. They dance and nearly kiss before she tells him he should leave.
While training the elephant, August uses the bull hook too aggressively for Jacob's and Marlena's tastes, but they keep silent. Later during Rosie's first performance, with Marlena atop her, August uses too much force to try to get a more exciting performance out of Rosie. Rosie freaks out and runs from the tent, forcing Marlena to grab a pole at the exit of the tent before being carried off on the stampeding elephant. Although the crowd cheers at Marlena's great gymnastic move, August is enraged. After the workers coax Rosie back to the circus, he takes the bull hook and beats Rosie with it. Jacob tries to stop him, but is held back by other workers, and Marlena stands outside Rosie's train car with her hands over her ears until Rosie's shrieking stops.
Later, Jacob discovers that Rosie is able to take commands that are spoken in German, and August couldn't be happier. All three of them go out to celebrate and, with August away from the table, Marlena and Jacob have a conversation about her past. At the end, she asks Jacob, Where were you when I was 17? The party gets raided (Prohibition Era), so Jacob and Marlena flee into an alley, far away from August. They share a kiss, but Marlena pulls away and tells Jacob not to follow her.
Jacob and Marlena act as if nothing has happened between them, it's business as usual, and the circus is selling out shows. During a surprise celebration for Jacob (due to him discovering Rosie's talents), August senses something a bit too intimate when he notices an exchange between Jacob and Marlena. Later, August discovers Marlena and Jacob at her tent, and confronts them in an unconventional way. Marlena almost has August convinced there is nothing between her and Jacob, but he rejects her story. A fight breaks out and Jacob is forced to jump off the train, but not before convincing Marlena to jump with him.
They find sanctuary at a hotel, and make love, but in the morning are discovered by August's henchmen. A bloodied and beaten Jacob regains consciousness only to discover Marlena is gone. He makes his way back to the circus and finds his closest work mates are not in their bunks. Knowing how August is, Jacob becomes enraged with thoughts of them having been killed (it is later explained they were thrown off the train, landed on a rock field, and did not survive). He sneaks into August's tent, to find Marlena lying with him. He has a knife in his hand and is about to kill August, but Marlena sees what he is about to do and convinces him otherwise. They meet the next morning and discuss their escape plan, which will be after the matinée act. While waiting for the show to be over, he hears the roar of the crowd change and rushes into the tent. The workers let the wild animals out of their cages, including the tigers and bears. This was done as payback for August's having had two of the workers (Jacob's closest work mates) killed. As the crowd rushes to get out, August encounters Jacob and begins hitting him with a pipe. Marlena sees what is happening, and tries to stop him, but is quickly taken down by August. He begins choking her, while his henchmen attend to Jacob, who is trying to get to Marlena. Rosie senses what is happening, just as Jacob begins speaking German to her, commanding her to pick up a spike and hit August with it. August dies.
Jacob becomes a licensed veterinarian, and he and Marlena get married and start their own act. The movie returns to the present day and older Jacob explains that he and Marlena had five kids, and they kept the horses and Rosie. After many years, Rosie passed away, and Jacob explained that Marlena cried for days as Rosie had been part of their lives from the beginning. The young man asked what happened to Marlena, and he told him she passed away in her bed, still beautiful. Jacob says that he was able to give her everything he ever promised her. Jacob then asks the man for a job as a ticket taker for the circus, saying there's nothing wrong with him other than that he is old. The man agrees, saying that Jacob will go down in the records book as the oldest man to run away with the circus. Jacob laughs and says, I'm not running away, I'm coming home.