Captain Vallo (Lancaster), known as "the Crimson Pirate", is the scourge of the Caribbean seas in the late 18th century. He and his men end up capturing Baron José Gruda (Leslie Bradley), a Spanish lord who's come to the islands to crush a rebellion led by a figure known as El Libre (Frederick Leister). Vallo gets the idea of selling the guns and gun powder on the ship to El Libre, and then sell him out for twice the price to the Baron. Except things don't quite go as planned, not least of which because Vallo ends up falling in love with El Libre's daughter Consuelo (Eva Bartok).
One of the best adventure and Swashbuckler movies of The '50s — and one that runs almost entirely on Rule of Cool and Rule of Funny — the film also marked the third and final collaboration between Lancaster and Siodmak, who had a falling-out during the film, but it marks a high point in both of their careers.
This film contains examples of:
- Anachronism Stew: Most of the inventions Professor Prudence comes up with, particularly nitroglycerin, hadn't even been invented yet. Doesn't matter, because the movie runs on Rule of Cool.
- Arranged Marriage: Consuelo near the end to the corrupt governor, until Vallo shows up to save the day.
- Antagonistic Governor: Bordering on The Caligula. Baron Gruda supposedly takes authority from a monarchy, but enjoys complete freedom to satisfy his greedy heart regardless - which he uses to do things like steal grain from the citizens to celebrate himself, and kill anyone for the slightest of reasons. In one particularly grim example, when a crowd of people reads one of his oppressive proclamations, and one tries to tear it down, he has that person killed on the spot for defacing property, and the entire crowd shot at for being "accomplices."
- Chronic Backstabbing Disorder: Humble Bellows. He even lampshades it at one point, saying it's a pirate's duty.
- Cigar Chomper: Ojo, even when he's disguised as a nobleman or in drag.
- Couldn't Find a Lighter: In the climax, Ojo uses the flamethrower cart to light his cigar.
- Disguised in Drag: Vallo, Ojo and Professor Prudence when they're sneaking into the wedding; except Vallo has to remind Ojo to cover his beard with flowers.
- Hard-Work Montage: Vallo helping the rebels build Professor Prudence's inventions.
- Heroic Sacrifice: Humble Bellows stays on Vallo's boat to make a diversion. He likely dies when Gruda's ship fires a broadside, which destroys Vallo's ship.
- Imperial Stormtrooper Marksmanship Academy: Throughout the movie (but, then again, Rule of Funny).
- Meaningful Name: Pr. Prudence. "Prudence" means "caution" in French. He is afraid when Vallo and Ojo manipulate the nitroglycerin.
- Mr. Fanservice: Vallo (Burt Lancaster), of course. The film even starts with a Shirtless Scene of him.
- No Communities Were Harmed: although the flag of Castile and Leon ◊ and the many Spanish names, both real (Consuelo) and fake (José Gruda), indicate that "San Pero y Cobra" are Spanish possessions, this is never stated outright.
- Only Known by Their Nickname: "El Libre's name is never specified.
- Rebel Leader: El Libre leads a rebellion against Gruda.
- Redemption Equals Death: Humble Bellows betrayed Vallo, and dies in a Heroic Sacrifice that allows the pirates to win against Gruda.
- Sex–Face Turn: A rare male version, with Vallo changing his mind about what to do with El Libre when he falls in love with Consuelo.
- Slipping a Mickey: Baron Gruda does this to the crew so he can double-cross them.
- The Speechless: Ojo, in order to disguise Nick Cravat's thick Bronx accent.
- Tap on the Head: One of El Libre's men knocks out both Vallo and Ojo by hitting them over the head with a barrel, which in real life would probably cause serious brain damage (but then again, Rule of Funny).
- Undying Loyalty: Ojo stays with Vallo no matter the circumstances.
- Walk, Don't Swim: Vallo, Ojo and Prudence use the capsized skiff as an improvised submarine and make their way to a shore by walking on the seabed, while making sure to spare as much oxygen as they can.
- Walk the Plank: Humble Bellows wants to make whoever they take prisoner do this.