Tony "le Stéphanois," a seasoned criminal fresh out of a five-year prison sentence for a jewel heist, finds himself struggling on the streets. His friend Jo approaches him with a reckless proposal from their mutual acquaintance Mario: a bold smash-and-grab at a Parisian jeweler's front window. Despite the allure, Tony initially declines. However, his heart grows heavy when he discovers that his former girlfriend, Mado, has been romanced by the notorious gangster and nightclub owner, Pierre Grutter, during his absence.
Confronting Mado at Grutter's club, Tony brings her back to his shabby flat, where his jealousy culminates in a brutal beating, reflecting his frustration at her involvement with Grutter. Driven by rage and desperation, he shifts gears and agrees to the heist—this time, with a twist. He proposes they not merely rob the window but aim for the far more challenging task of cracking the store's safe. The group decides to bring in César, a skilled safecracker from Italy, to help enact their ambitious scheme. Together, they meticulously plan and rehearse their daring operation to disable the sophisticated alarm system.
The heist kicks off under the cover of darkness as they begin chiseling through the cement ceiling of the store from an adjacent flat. The tension mounts as the plan unfolds smoothly, and the criminals manage to escape without leaving a trace. However, unbeknownst to his accomplices, César steals a diamond ring to gift to his lover, Viviane, a singer at Grutter's venue. Their caper soon grabs the headlines, and the men arrange to fence the stolen jewels with a contact in London.
In a twist of fate, Grutter discovers Mado's injuries and, feeling betrayed, she leaves him. In retaliation, Grutter orders his drug-addicted brother, Rémy, to kill Tony. Yet, a clue—a diamond gifted to Viviane—leads Grutter and his thugs to realize that Tony, César, and Mario orchestrated the jewel theft. They promptly force César to confess. Instead of claiming a hefty police reward, Grutter decides to take matters into his own hands, leading to a tragic turn of events as Rémy brutally murders both Mario and his wife Ida, who refuse to divulge the location of the loot.
Devastated, Tony retrieves the hidden treasure from the couple's apartment and anonymously provides a lavish funeral for them. In a race against time, he confronts Grutter and discovers César’s betrayal, leading him to coldly execute César for his disloyalty.
Meanwhile, Grutter's gang kidnaps Jo's young son, Tonio, to pressure the group. When the London fence arrives with the ransom, Tony makes a brave decision to rescue Tonio, telling Jo that violence is their only option. With assistance from Mado, he tracks down the boy to Grutter's secluded house, resulting in a lethal showdown where Rémy and Louis meet their demise.
However, upon returning to Paris, Tony learns that Jo has broken under the pressure, leading to a tragic meeting with Grutter. In a cruel twist, Jo is killed before he can save him. In a final confrontation, Tony faces a gravely wounded Grutter, ultimately killing him, but not before suffering fatal injuries himself.
With moments to spare, Tony drives erratically back to Paris, ensuring Tonio is safely returned home. As he succumbs to his wounds, police and bystanders encircle him and discover a suitcase containing an astounding FF120 million in cash. Jo's wife, Louise, takes Tonio from the car, leaving the tragic scene behind, as she relinquishes the suitcase and Tony's lifeless body to the authorities.
