Plot

On the 10th anniversary of his father's death, Giovanni reluctantly accepts the task of bringing a cake to the home of his uncle, a mob boss, for a celebration. Just two hours into the night, Gio's life is forever changed.

The Birthday Cake begins with the 10th anniversary of Giovanni's father's death, Giovanni reluctantly accepts the task of carrying on the family tradition of bringing a cake to the home of his Uncle Angelo, Brooklyn's last Mafia boss, for a celebration. Just two hours into the night, Giovanni's life is forever changed and he's forced to grow up after witnessing murder, violence, chaos and the truth about what happened to his father.

In New York City, Gio's father Sam has been killed and his mother Sofia doesn't want to get out of bed, so Gio wants to get out of the house. He brings some of the food that was brought to his house to the church.

Gio's cousin Leo is riding with Uncle Ricardo. They see a man with several bikes and Ricardo asks him if those are his bikes. When the man doesn't give a satisfactory answer, Ricardo stops the car, chases the man and beats him up.

Gio lights a candle and talks to Father Kelly, who asks what happened to him. Gio says some Russian guys at school beat him up. After a conversation with Father Kelly, he leaves the church. The weather forecast says snow, but Gio isn't dressed for it. Leo gets out of Ricardo's car when he sees Gio and gives him a jacket. Leo and Gio walk together and when they run into the Russian guys, Leo gives Gio a gun and some of them run away, but another one does not.

Ten years later Gio is getting dressed up for a family celebration. Christmas decorations are up everywhere, but that's not the only reason for the celebration. Sofia doesn't want to go, even though the tenth anniversary of her husband's death is being observed. She does, however, give Gio the birthday cake she always makes each year. Sofia also comments on how Leo has done so much for them but he isn't doing what he should to keep in touch with other family members. She also criticizes Uncle Angelo for not keeping in touch with the family. Sofia insists Gio stop by the church that night to light a candle.

Occasionally, Father Kelly's voice is heard explaining important details. His first time, he says Leo did time and now he is out, and his help for Gio and his mother came from being a dirty cop.

Two tough looking guys confront Gio. One got out of an HVAC repair van which appears later. Gio calls Leo on his cell phone saying the FBI is looking for him.

Gio was told to bring butter to the family celebration. When he stops at a bodega, a punk rocker type is making trouble, and then he is told by a store employee that the employee's father was threatened because he wouldn't sell the store. Now the refrigerator isn't working. Gio can't get butter.

At a bar where Leo is supposed to be, Peeno is outside taking a smoke break, and a group of women having a party goes out to a limo. One is wearing a bridal veil. Later, one member of the group gets angry she was left behind. Gio and Peeno have a conversation where Peeno points out some suspicious guys.

Gio stops by Leo's place but Leo isn't there. Very loud rap music is playing and a dog in a cage is barking. Then Peeno comes in with some Puerto Ricans who are looking for Leo and they intend to do something to him. Leo hides and Peeno sees him but doesn't say anything.

Gio's best friend Tommy has a bakery and Gio stops there. Tommy has an attitude and suggest he hates everyone, including Gio. His partner Diane is nicer, and when she sees the cake decides it needs a box. Gio explains it is his father's birthday, but Diane didn't realize Gio's father is dead. Gio later asks Diane out. Tracey shows up after the bakery closes, and when she and Tommy get in a car driven by a Puerto Rican, they offer to let Gio go with them. The driver is annoyed by Tommy's references to the bad Puerto Ricans, but Tommy doesn't care.

At a strip club, Gio has a conversation with Uncle Tony, and Cousin Joey makes trouble.

Gio arrives at a nice house and everyone is glad to see him, and the cake. As Father Kelly explains, Uncle Angelo has given parties for people in the neighborhood and he is well-liked, though he was shot and now has trouble talking. Subtitles are necessary to understand Uncle Angelo as he speaks with an electrolarynx. Gio says hello to Uncle Carmine, who is on oxygen and watching "A Christmas Carol", and won't even acknowledge he has a visitor.

Uncle Ricardo demands to know about Leo and pulls a gun when he doesn't get an answer. He is asked to leave, even when he protests that he is a cop and allowed to have a gun. When some mysterious men show up, it is explained to Gio that it is boys' night because all the women are at a bachelorette party. The family has a nice meal and Vito toasts Gio's father, who is depicted as a saint.

A close-up of the box with the cake is accompanied by ominous music, as if the box contains a bomb. Later, someone realizes the cake needs to be served. Gio declines to eat since he is allergic to chocolate. The knife to cut the cake is passed from one man to the other with that ominous music again. The other men eat and they end up getting very sick. Gio realizes they are all dying, and after speaking to Uncle Carmine, who makes an offensive remark, Gio runs out and heads for Leo's place.

The Puerto Ricans and the dog are dead. Ricardo has gun on Leo, who is in a bathtub covered with blood and looking frightened, and Ricardo is demanding information. Gio fights Ricardo and tries to save Leo but it is too late.

Gio returns to the church very upset. Father Kelly comforts him and says he knows what is going on, and thanks Gio for painting the church all night. Then Sofia comes out and hugs Gio. She refuses to explain when Gio asks what happened, but just continues to hug him. After Gio lights the candle, he and the others leave.