The story starts on a Saturday summer afternoon in 1912. In the small yard among the old houses of Williamsburg, Brooklyn, a tree, called the Tree of Heaven grows, offering the inhabitants shadow and inspiring deep thoughts. Francie Nolan, one of these inhabitants is eleven years old. She with her little brother gather garbage for some money. Every day Francie wakes up with her family, her father Johnny and her mother Katie and looks at the Tree of Heaven before going to the work. Johnny is young and handsome, with prominent Irish blood. He works in the restaurant nearby as a waiter and sometimes sings at the evenings to earn some extra money. His wife Katie is the main breadwinner in the family, she works as a janitor in the building in exchange for rent of their tiny apartment. Despite her harsh life, Francie loves her family, her life and the tree nearby. The Saturday described at the beginning of the story is quite average for the girl: she completes a dozen of errands for her mother, as always, goes to the library to read something interesting and then returns home, watching the life of her yard and neighbors from the fire escape. The atmosphere in the Nolans’ house is full of love and warmth, so Francie loves to return home and be with her family.
The story suddenly returns us to 1900 via flashback, to the day of the first meeting of Katie and Johnny. Katie was the factory worker at that time and befriended her colleague, another young girl named Hildy O’Dair. Hildy’s boyfriend was a young handsome Irish man named Johnny Nolan. Soon they broke up and Katie ended up dancing with Johnny. When they danced, she suddenly understood that she was thinking about spending the whole life together with him. They immediately and mutually fell in love and married half a year after. Katie is a strong and determined woman, who was raised by the other strong and determined women to be able to take care about herself and her family. Johnny is her complete opposite. He is talented, but careless and weak, up to the point of being airhead, but he was adorable and they complemented each other perfectly.
While still very young and facing the hardships of married life, Johnny and Katie had to work a lot to survive. At first, they were janitors in a public school together, but when Katie got pregnant and wasn’t able to work as much as before, things became even more complicated. A year after having Francie Katie gave birth to her brother Neeley. Neeley became her favourite of the two, but unable to earn enough to support both his wife and two babies, Johnny became weaker and more depressed and dependent. Katie, otherwise, decided to fight and managed to keep the house, look after the kids and work to support the family. Johnny started to abuse alcohol, trying to escape from his poverty and powerlessness. At his twenty-first birthday, after his ugly drunken behaviour disgraced all the family, the Nolans had to move away to live separately. Their new apartment was situated on Lorimer Street and was lovely. The family lived there until a new shameful event happened, this time caused by Katie’s sister Sissy. They had to move again, to the house on Grand Street, where the Tree of Heaven grows.
Francie and Neeley went to school together and the same year. Francie loved to study very much, but her willing to attend school was greatly diminished by the social segregation and cruelty she saw amongst her classmates and teachers. The teachers scolded and punished the poor children, allowing the rich ones to do what they please, even if it offended the others. Returning home one day, Francie saw a beautiful school and started dreaming about attending it and learning happily without mocking and cruelty. She told about her dreams to her family and Johnny, who still preserved his creativity, came up with a way to transfer his daughter to that school. It appeared to be better indeed, with no segregation and no appealing to social status. Despite Francie didn’t make many friends with her shyness, the school again became a pleasant experience for her. Francie and her brother grew up. They spent their holidays together with their parents and enjoyed that time much.
The book returns to the present and we see that it is the time of coming of age for Francie. She gradually loses her innocent and naive demeanor, becoming aware about the harshness of the world. The first episode that causes it is connected with a local ritual of tree-throwing. One Christmas Francie and Neeley participate in such a ritual, trying to catch the Christmas tree that is thrown. They are excited with the thought of a Christmas tree, but they realize the real danger too late - the tree thrown at them is huge and they are just two small children frozen on the spot with fear. The kids don’t understand what could happen fully, but we, as readers, see how cruel the ritual was. Katie starts to worry, wondering what would happen when her kids knew about the harsh condition they live in and bleak fate that awaits the poor people like them.
Another events that shakes Francie’s innocence happens when she is almost caught by a sex offender. Terrified, the girl runs home, chased by him. Luckily for her, Katie has a gun at home and shoots the man. Francie escapes the danger safe, but she is traumatized with her first experience with sex. Soon, after she has a talk with her mother and starts her period, Francie starts to understand the vulnerability of women and the taboos surrounding their sexuality.
Growing up, Francie understands that her father has issues and is dependent on alcohol. She notices that as the years pass, Johnny comes home drunk and without any money more and more often. Gradually, her father becomes a worthless worker and is finally kicked away from the Union. This is the last straw for him and desperate, Johnny gives up, only drinking and wandering around. To make the situation more complicated, Katie is pregnant again with their third child. Unfortunately, Johnny dies because of alcohol intoxication before his daughter, Anne Laurie, is born.
The death of her father strikes Francie deeply. She was a faithful Catholic before, according to her family Irish tradition, but now she rejects God in anger for letting that happen. Also, before she tried her best to write cheerful and good English compositions, out of respect to her English teacher. But now she feels an urge to express herself in other way and starts to write scary and ugly, though still grammatically correct compositions. Despite her teacher’s disapproval, Francie refuses to return to her previous style of writing and, when asked to burn the “bad” compositions, she burns her earlier ones instead that were overly sweet and flowery. Francie feels that these compositions reflect her personality no more and wants to decide for herself who she is and what a writer she can be. This is an important step for her on the way of growing her identity.
Francie may look like a rebellious teenager in her school and church, but deeply inside she regains her kind and caring personality. She is able to empathize and enjoy life. Francie patiently helps her mother after her delivery and, despite the conflict of generations and her teenage delinquency, Francie respects her mother and understands how hard it is for Katie to be left a widow, without a husband she still loved. Still, Francie loves her father very much also. Her pragmatic mother can never substitute her dreamy and creative father for her. Katie’s sister Sissy comes to help Katie with children, she befriends Francie and goes along with her up to the school graduation. On her graduation celebration Francie receives red roses from her father - it appears that Johnny, understanding that he cannot keep the money intact, gave it to Sissy, asking to buy flowers when Francie will have her graduation. Francie breaks down and cries, grieving her father, her innocence and herself, so hurt by the loss.
Katie now has to care for the baby, so she can’t work to support Francie and Neely. So, after they finish their eighth class, both siblings have to work during all the summer. Francie, as her mother before, starts from the position of a factory worker, but then finds a better job in a clippings bureau. She loves her new job, because she can read the news from all over the country and learn how the world around her is operating. When they get their first payment, the siblings present it to their mother, proudly feeling themselves the new breadwinners of the family.
Katie has a good job and she likes it still, but she desperately wants to attend high school and learn more. But Katie decides that the boy will achieve more than she and sends her favourite child to high school instead, because the family has money to pay for the one child only. With Francie working the family now can allow more and live the more relaxed life. Francie doesn’t hold a grudge and enrolls to college summer classes herself.
With the beginning of the World War I the life in America and in the world changes. Sissy, who has poor health, now can give birth to a healthy baby due to the technical and medical progress. Francie feels the romantic love for the first time: she meets a young soldier named Lee Rynor and immediately images a brave war hero. She falls in love with him immediately, but Lee has a fiancée, who he returned to marry before going back to war. Francie is heartbroken for a long period of time, until, surprisingly for herself, she understands that she feels very comfortable in the company of the neighborhood boy (who is now a young man) Ben Blake from her summer school.
The novel ends with Katie also meeting her love. Sergeant McShane, who returns from the war, admits his feelings to the widow and makes her a proposal. He is a decent and generous man and he promises to take care about little Laurie and pay for college for both Neeley and Francie. Katie happily agrees to marry him and the day before the wedding all the family moves from their cramped apartment to the spacious one. Francie prepares to leave for Michigan to study in the college and says her farewell to the Tree of Heaven. She feels that the Tree also says farewell to her.