In an unspecified European country, the story unfolds around the clever and daring activities of John Phillip Law, who plays the notorious master thief Diabolik. He expertly orchestrates a series of high-stakes heists and audacious plans that keep law enforcement, especially Inspector Ginko, on their toes. The film kicks off with a meticulously planned operation to transport $10 million from a bank, where police chief Claudio Gora and his team attempt to outwit Diabolik. To do so, they create a diversion—using a truck filled with wastepaper to distract from the real shipment—while Diabolik swiftly takes the money in a lavish Rolls-Royce, escaping just before the police can catch him.
Diabolik’s life is filled with thrill and danger, and he shares an intimate yet perilous relationship with his lover, Eva Kant, played by Marisa Mell. The two are shown in an intensely private moment, celebrating their loot and love atop their underground hideout. Their partnership is a perfect blend of trust and cunning, as they share moments of passion amid the chaos of their criminal pursuits. Their daring lifestyle takes them to a press conference convened by the Minister of the Interior, a character portrayed by Terry-Thomas. During the event, the Minister imposes the death penalty to discourage criminals like Diabolik, but the duo isn’t fazed—they disrupt the conference by releasing a gas that causes excitement and chaos among the attendees.
In their quest for luxury and thrill, Diabolik and Eva set their sights on the infamous Aksand emerald necklace, stored in the Château de Saint-Just. Learning about Eva’s whereabouts from a prostitute, Valmont—played by Adolfo Celi—circulates an identikit image of her, sparking a dangerous manhunt. Undeterred, Diabolik infiltrates the castle, scaling its treacherous walls, and executes a flawless theft. Though they escape by pulling off a clever deception—using mirrored film on the road and dummy decoys—Eva gets wounded during the escape, highlighting the real dangers they face.
Their criminal activities escalate when Eva is recognized from the identikit during a routine visit to her doctor and is abducted. Diabolik, always resourceful, decides to trade the stolen necklace and the $10 million on a plane owned by Ralph Valmont, a character who initially appears as a dangerous gangster but then becomes an uneasy ally. Diabolik boards the aircraft, only to be ejected—yet he manages to grab Valmont just before a bomb, planted earlier, detonates. As chaos ensues, he rescues Eva from captivity, culminating in a tense confrontation with Valmont, whom Diabolik kills by firing a magazine filled with emeralds at him.
At this point, Diabolik’s cunning extends to feigning death—a technique learned from Tibetan lamas—by taking a mysterious capsule. While public records and police prematurely declare him dead, Diabolik’s true escape plan involves sneaking out with Eva, who helps administer the antidote, restoring him to life within twelve hours. Disguised as a nurse, Eva helps him slip past the police, and Diabolik returns to his secret lair, retrieving Valmont’s ashes that contain valuable emeralds and escaping once more.
The story then takes a larger scale with Diabolik and Eva stealing twenty tons of gold, which is melted down into a single block to prevent theft. They execute a daring plan to thwart the authorities during transport: causing a train carrying the gold to explode by placing a bomb, resulting in the gold plunging into water. The police, led by Inspector Ginko, relentlessly pursue Diabolik, believing him to be dead after an escape gone awry, with Michel Piccoli portraying the determined inspector. In their pursuit, the police track Diabolik’s hideout by following the trail of molten gold, which covers the entire cavern after a botched attempt to melt the gold into smaller ingots under fire from the police.
Amidst the chaos, Diabolik, clad in his heat-proof suit now coated in gold, is believed to have been killed. However, in an ultimate display of his ingenuity, he fakes his death once again, this time using a capsule that requires an antidote within twelve hours. Eva, caught between loyalty and love, administers the antidote by disguising herself as a nurse, allowing him to escape from the authorities unnoticed. Later, Diabolik returns to the morgue to retrieve the emeralds from Valmont’s cremated remains and leaves with Eva, continuing their illicit adventures.
In retaliation, Diabolik places a hefty reward for his capture, prompting the police to blow up tax offices, and causing national financial chaos. The government’s inability to recover or demand taxes plunges the nation into debt, symbolized by a single massive gold block, which is transported on a train. Diabolik and Eva execute a daring maneuver, sabotaging the train with a bomb after diverting it, causing the gold to fall into a river. The climax features Diabolik’s cleverness once again as he escapes from a police trap, with his gold thoroughly melted into molten pools. His heat-resistant suit, now coated with molten gold, leaves him presumed dead, yet he reveals a wink to Eva before disappearing into the shadows.
The film ends with Diabolik and Eva in their hidden world, constantly evading capture through wit and resourcefulness, embodying the ultimate antihero—charming, ruthless, and unstoppable.
