We begin with a cat on the streets of Paris who,after hearing the milk truck pass by, heads down to a basement apartment through a pet door and licks the face of the sleeping Gigot (Jackie Gleason), the poor mute janitor who lives there. He gets up, gives the cat some milk and then does his morning ritual of prayers, eating some bread and washing his face from water draining from a pipe.
Two investigators from the Department of Complaints visit an old woman who called them. She complains that Madame Brigitte next door has hired a simpleminded janitor who steals her milk and ash can and sweeps leaves in front of her residence. She wants him committed. Gigot steps out and indeed sweeps up some leaves, careful to get each one and deposit them in the trash. He even stops to pluck dead leaves off the tree. The investigators nod and go in to start the paperwork.
Gigot goes to Madame Brigitte (Gabrielle Dorziat) for his salary. She complains he hasn't earned it, but set the coins out for him then takes deductions for a broken window, messed up commode and even for replacing his worn-out broom. He leaves with just a few coins. Outside, mischievous men distract him so a kid can attach a tail to his back. The neighborhood laughs until a kind policeman removes it. Gigot goes to a pastry shop admiring the cakes, but just buys some stale, broken cookies. He mostly shares them with friendly dogs who follow him, and even gives some to a cat and a horse.
Madame Brigitte tells the investigators that Gigot is as sound-minded as anyone else. She does admit he has a habit of attending other peoples funerals, helping the mourners mourn. Shortly after that, Gigot sees a funeral procession going down the street. He follows them and attends the service, comforting the bereaved and behaving reverently the entire time.
That night, the same mischief-makers from before are at a bar. They see Gigot coming and decide to have some fun. They offer to feed him on the house, but first he must have a drink. Then one bets 5 francs he can't down a large glass of pernod without taking a breath. Gigot manages to drink the entire glass down. Then the bettor's friend insists he must have a chance to win back his money. So Gigot is conned into drinking a glass of eau de vie this time. When he finishes, he is drunk and loses interest in eating. Instead he pantomimes some of the people he saw at the funeral, and then stumbles into the next room where he begins to dance with a pretty girl. But the alcohol hits him and causes him to collapse against the wall. He gets up and humbly exits the bar. The patrons all feel bad for a few long seconds, and then go back to drinking and dancing.
Gigot wakes up on the street in the rain hours later and begins to walk home. On the way, he spots a little girl Nicole (Diane Gardner) about 5 years old hiding under an archway. She backs away from him to another archway where her mother Colette (Katherine Kath) is also hiding from the rain. He takes them both to his apartment, sets out their wet coats to dry and gives them each a place to sleep.
The next morning, the cat-waking cycle repeats itself, only the cat ends up licking Colette's face. She screams and scares the cat away. She tells Nicole they are leaving, but Gigot offers them some bread so they stay for breakfast. Brigitte comes down the stairs and finds them all, asking Gigot when he got married and telling him to get to work to feed his new family. Colette again says they must go, but finds herself still coughing from the effects of last nights rain and weakly crawls back into bed.
Gigot is clearly enchanted with little Nicole and tries to amuse her with some sleight of hand tricks. When none of them work, he cuts a small piece of cheese and gives it to her. He then shows her a secret door leading down a corridor to another room. There he acts like a waiter, sets a table, and then has her put the piece of cheese on it. A mouse crawls from a hole next to the table and slowly eats the cheese. Nicole laughs uproariously and kisses Gigot on the cheek. Later he plays some records for her on an old gramophone, and dances to them.
That afternoon, he takes her on a ride in a wagon. He is distracted by a passing funeral parade, and when he looks back Nicole is gone. Fortunately, she has just gone into the church next door. He goes in and tries to answer her questions about who the statues represent. Eventually, he is frustrated with his inability to speak to her and starts to hit himself. But she makes him stop and they walk off together.
He takes Colette and Nicole to the amusement park. Colette stays on a park bench while they go on ahead. Nicole wants to ride the carousel. Gigot sets her on the horse, but he only has enough for one fare so he is not allowed to hold her as she rides. Instead he runs around the outside of the carousel to keep an eye on her, bumping into people and falling over hurdles as spectators laugh. She finally emerges from the carousel unharmed and asks to ride again.
Meanwhile Colette, who is a prostitute, is approached by a customer. She pretends to be there alone and lets him make advances to her. When Gigot returns, he thinks she is being attacked and runs to defend her. He ends up being beaten up by the man and his friend until a policeman arrives to break it up. Colette tells the policeman Gigot is not her husband and she takes Nicole and runs off. When the policeman finds out Gigot is mute, he just sends them all on their way.
When Gigot returns home, Nicole and her mother are still there, but preparing to leave. He indicates he is willing to pay them to stay (by pantomiming handing out money.) She gives him one hour to produce some money, or they will leave. He wanders the street and sees that the baker and his wife are distracted watching a painter. He sneaks in the bakery and steals a bag of money from the money box. He also takes some stale cookies, but leaves a couple of coins in payment.
He returns to the apartment and shows Colette the money. She is impressed and declares they are going shopping. They buy Nicole some dresses, a new outfit for Colette and even a new hat and coat for Gigot. As they walk down the street in their fancy clothes, people speculate that he has a rich relative or won the lottery. They go to a restaurant and he flashes his money. They are given the best table in the house. Colette orders champagne and Gigot indicates champagne for all. The patrons are delighted. But later as Gigot dances with Nicole, Colette is approached by her former lover. He sneaks her outside and declares he is willing to take both her and Nicole back, despite claiming before that Nicole was a burden. She agrees to meet with him after Gigot falls asleep.
Later, Gigot pays the bill and leaves the change as a tip. He takes his two guests home. Late that night, Colettes lover whistles for her. She comes out, planning to sneak back in and get Nicole. But he tells her tonight is just for them; let Nicole stay "with the dummy". From a distance, Gigot sadly watches them sneak away.
The next morning, we again see the cat going to Gigot's apartment. But this time, no one is there. Outside, the two investigators arrive declaring they are going to have Gigot committed. Suddenly, Colette comes out of the apartment screaming that her child is gone and Gigot must have kidnapped her. The townspeople enter into the apartment and the baker finds his money bag and realizes Gigot is the one who robbed him.
Meanwhile, Gigot and Nicole are actually safe in the secret room, where he is playing records on the gramophone and dancing. Suddenly, the ceiling collapses on them. Gigot emerges from the rubble and finds Nicole unconscious with a gash on the side of her head. He clears the rubble away and carries her out the back way unseen by any of the townspeople. He takes her to the church, where the priest sends for a doctor. The doctor treats the gash and says she is just shaken up. She murmurs "Play the music, Gigot," over and over. Gigot rushes back to the room and retrieves the gramophone. Some townspeople see him and give chase. Eventually, he ends up near a coal refinery where he accidentally drops the gramophone onto a conveyor belt. He climbs on the conveyor belt to retrieve it, riding it up and then sliding down a coal chute into the river. Just then, a tugboat sails by right over the spot where he had fallen in. After it passes, only Gigot's hat floats to the surface. A townsman grabs the hat and declares that is all that is left of the man. Unbeknownst to him, Gigot is hiding in the water almost at his feet.
The townspeople gather with Colette, Nicole and the priest and learn the whole story behind Gigot's theft and the apparent kidnapping. The priest assures Nicole that Gigot died trying to save her. Everyone feels guilty about how they treated the poor janitor. They decide since he liked funerals so much, they will throw him the biggest funeral the town has ever had.
Later, they townspeople all gather for the funeral with lots of flowers, a hearse, and even a small band. Gigot sees the procession and follows at a distance, later hiding in a tree at the cemetery. It is not until the mourners start to speak that Gigot realizes the funeral is for him. Brigitte says he was a treasure who did the work of three men. The townsmen praise his drinking ability and the investigators claim they were always on his side. Everyone throws flowers on his grave, beginning with little Nicole. Then they slowly walk away. He climbs down from the tree and tries to signal them, but of course cannot. Just as he is turning to leave, one of the townspeople sees him and calls out to the others. Instinctively, Gigot flees. The movie ends with the whole town pursuing Gigot, who is unaware that now they all just want to be his friends.