Thief Roger Sartet (Alain Delon) joins Sicilian mobster Vittorio Manalese (Jean Gabin) to rob a jewelry exhibition in Paris. When the jewels transfer to New York, Vittorio decides to hijack the airplane transporting them. Le Goff (Lino Ventura), a policeman with a grudge against Sartet, tries to unravel the plot before it comes to fruition. When Sartet starts an affair with Vittorio's daughter-in-law Jeanne (Irina Demick), things grow more complicated.
The Sicilian Clan offers a complicated international chase through France, Italy and the United States. Verneuil (working from Auguste Le Breton's novel) keeps things relatively smooth, with intense, smoldering atmosphere overtaking story points. He stages tense action scenes - Sartet's escape from a police van, a hotel standoff, a finale modeled on The Killing - with faultless verve, but the main appeal is watching the crooks operate.
The centerpiece is the airplane heist, filmed with the precision of Le Cercle Rouge's central robbery. Eating up nearly half an hour, it's impeccably paced, staged without music or unnecessary intrusion. Sartet impersonates an American investor, carrying off the robbery without a hitch - until his mark's wife (Sally Nesbitt) nearly spoils everything. Cops and ground control in France and the US scramble to catch the plane, but the mobsters outwit everyone. It's a bracing scene that renders the final 20 minutes anticlimax.
Clan immerses viewers in its seedy world, where the close-knit mobsters (Vittorio enlists his children in the heist) seem more likeable than cops like Le Goff, who beat informants and entrap suspects. Verneuil paints his protagonists with broad, eccentric strokes: Le Goff trying to quit smoking, Vittorio serving his grandson spaghetti, Sartet seducing Jeanne by killing an eel. Ennio Morricone's score adds a playful note, pairing ominous whistling with boingy marranzano.
Alain Delon plays another variant on his usual stoic criminal, charisma compensating for a thin characterization. Jean Gabin's Mafioso is more compelling, a grouchy, protective patriarch obsessed with loyalty. Lino Ventura gives his stock inspector role a rough edge, determined but unscrupulous. Irina Demick is an appealing love interest and Sydney Chaplin has an amusing role as a gangland contact.
The Sicilian Clan's deliberate pacing may put some viewers off, but it's worth sticking out to the end. Naturally the "perfect job" ends in betrayal and murder, but here driven more by personality than greed. It results in a denouement tragic yet immensely satisfying.