The story in this novel is told as a series of memories by a ninety-three year old man called Jacob Jankowski. Jacob lives in a nursing home where every moment of his life is controlled by the staff, and he is told what to eat, what to do and how his day will be spent. When his memories begin, we are introduced to twenty three year old Jacob, a Polish American preparing for his finals at Cornell University where he is studying veterinary medicine. He receives the devastating news that his parents have been killed in a car accident. Jacob's father was a veterinarian and Jacob had planned to join him in the practice after graduation. Jacob learns that his parents' home was mortgages to the hilt to pay for his expensive Ivy League education; he will not inherit the home and this precipitates a breakdown. Just before graduation he leaves Cornell jumping on a train in the middle of the night. The train belongs to the Benzini Brothers Most Spectacular Show On Earth. When the circus owner, Uncle Al, learns that Jacob has veterinary training he is hired to care for the circus animals. Jacob finds himself sharing living quarters with a dwarf named Walter, whom the Circus call Kiko, and Walter's dog, Queenie.
A few weeks later Jacob is summoned to take a look at Camel, a man who has been drinking Jamaican ginger extract for many years and as a result cannot move his arms or legs. Fearing that Camel will be thrown off a moving train, a punishment known as "red-lighting", Jacob hides him in his own quarters.
August, the Equestrian Director, is a brutal man who mistreats the people around him and also mistreats the animals in his care, especially Rosie, the new elephant. However when he chooses to August can also be gregarious, generous and affable. Jacob develops a guarded relationship with August but falls in love with August's wife Marlena. August grows suspicious of their relationship and beats both his wife and Jacob. Marlena leaves August and stays in a hotel whenever she is not performing with the circus. Uncle Al informs Jacob that August is a paranoid schizophrenic and issues Jacob a threatening ultimatum; bring August and Marlena together again as a couple, or both he and Camel will be red-lighted.
A few days later, Jacob discovers that August has tried to see Marlena so he visits her at the hotel and comforts her. They sleep together, both declaring their love for each other. Marlena returns to the circus to perform and continues to meet with Jacob in secret. She refuses to allow August anywhere near her which angers Uncle Al. She also discovers that she is pregnant.
One night Jacob climbs the train from car to car whilst the train is moving, jumping to August's room whilst carrying a knife between his teeth. His intention is to kill August but backs out and returns to his car, leaving the knife on August's pillow. However his car is empty with only Queenie waiting for him. Jacob realizes that Walter and Camel have been red lighted, as he would have been if he had been in his car as expected.
Later, several red-lighted circus workers return to release the animals, causing a stampede during a performance. As panic and chaos ensues, Rosie, the elephant who has born the excesses of August's brutality, takes a stake and drives it into August's head. His body is trampled in the stampede with only Jacob witnessing what happened. The circus is shut down and shortly afterwards, Uncle Al's corpse is found with a makeshift garrote around his neck. Marlena and Jacob leave, taking many circus animals with them, including Rosie, Queenie and Marlena's horses. They begin a new life together, joining Ringling's Circus. Years later Jacob becomes the veterinarian at Chicago's Brookfield Zoo and they settle in the Windy City, raising a family.
Back in the nursing home, Jacob is waiting for one of his children to come and take him to the circus. We learn that Jacob and Marlena married and raised five children. A few years before Jacob was put into the nursing home Marlena passed away. Sadly Jacob realizes that nobody is coming for him after all, so he slips our of the nursing home himself and makes his way to the circus that has set up next to the home. He meets the manager of the circus, a kindly man called Charlie, and begs to be allowed to stay with the circus selling tickets. Charlie agrees and Jacob believes in his heart that he has finally come home.
