Billy Dannreuther (Bogart) was at one point wealthy, having once owned an Italian villa and a restaurant, but he lost his fortune for reasons that are unexplained. Now he is working for three unscrupulous adventurers—Peterson the English crook (Robert Morley), Julius O'Hara who despite his name is German (Peter Lorre), and the generally mysterious Ravello. Peterson, O'Hara, and Ravello have engaged Dannreuther to use his contacts to help them acquire a tract of land in British East Africa that is believed to contain very very valuable uranium deposits. Dannreuther's employers are bumbling idiots, but they're murderous bumbling idiots, having already arranged the murder of a British colonial officer that they thought might expose them. Their hitman, Major Jack Ross, is accompanying the party to Africa, and looms as a very serious threat to Dannreuther if he steps out of line.
While waiting in Italy for a ship to Africa, Dannreuther and his comrades meet a British couple, Harry and Gwendolyn Chelm. Harry is a perfectly ordinary Englishman traveling to Africa to take possession of a coffee plantation that he's inherited. However, Gwendolyn (Jones) complicates things when she tells a fanciful lie that Harry's plantation has uranium deposits, which attracts the attention of Dannreuther's employers. Things get further complicated when Gwendolyn, who seems indifferent to her husband, falls in love with Dannreuther. Things are further complicated by the presence of Dannreuther's gorgeous Italian wife Maria (Lollobrigida), who falls in love with Harry.
- Abandon Ship: The gang is forced to do this in a hurry when the ship starts sinking. Ironically, a shot at the end of the movie reveals that the ship actually stayed afloat.
- The Alcoholic: The ship's captain, perpetually drunk, even when his rickety boat is adrift and taking on water in the middle of the Mediterranean.
- Bilingual Bonus: "Chelm" is the name for a legendary Jewish town ruled by "wise fools" who come up with silly solutions that usually somehow work out and fix problems. Highly appropriate for Harry Chelm—see The Fool below.
- Conspiracy Theorist: Major Ross has the standard set of beliefs about shadowy conspiracy types running the world.
- Driving a Desk: Seen as Billy drives Harry and Gwendolyn around the Italian village.
- Fake Aristocrat: Harry—sort of. As Gwen points out, he never passes himself off as an aristocrat or makes any pretensions. However, the manner of his speech and conduct and his Stiff Upper Lip demeanor lead people to assume that he's some sort of aristocrat. Gwen plays off of this when she starts telling tall tales about Harry being a lord and part of a very influential London family.
- Fainting: Maria is prone to this, like when she finds out that Billy survived the car wreck, or when she finds out that Harry survived the shipwreck.
- Fanservice: Besides Jones's She's Got Legs scene, Lollobrigida is packed into some incredibly tight dresses throughout the film. This leads into absurdity sometimes, like when the gang is staggering onto an African beach from a lifeboat, and Maria is still wearing a tight white dinner dress.
- The Fool: Harry Chelm is a classic type. He goes about in blissful ignorance, completely missing his wife's affair with Billy until she tells him, blowing off all of Billy's well-meaning advice. Once the bad guys steal his attache case onboard the ship, he starts barking threats about how he's going to turn them all in when they make landfall, in complete obliviousness to the fact that the bad guys thus have every reason to kill him. Sure enough, they try to, and Harry is just barely saved at the last second by Billy. Gwen then labels him a paranoiac in order to save him from being murdered, but he is put in irons onboard the ship—which leads an offended Harry to jump ship and attempt to swim to land. And he makes it, and takes possession of the land that the bad guys wanted, and strikes it rich.
- Have a Gay Old Time: "First, you made love to me."
- How We Got Here: The film opens with Peterson, O'Hara, Ravello, and Ross being marched down the steet in cuffs. Then it jumps back to the start of the story.
- Love Dodecahedron: Billy and Harry's wives each fall in love with the other man.
- Reports of My Death Were Greatly Exaggerated: Peterson and Dannreuther are pushing a broken-down car along a mountain road when it gets away from them and careens off a cliff into the sea. They are reported as dead, which surprises them when they return. Besides being funny, this is plot-relevant: Harry finds out about the uranium scheme when Rovello, believing his partner to be dead, approaches Harry and tries to get him to join.
- Same Language Dub: Some of Bogart's dialogue—apparently no one's sure how much—was dubbed by an unknown Peter Sellers after Bogart was in a car accident that damaged his bridgework.
- Scare Chord: A hilariously over-the-top, loud use of this trope when Harry tells the conspirators that he knows about the uranium scheme.
- She's Got Legs: Surely the only reason for the scene where Gwen is shown in the crow's nest of the boat, stretching her long, shapely legs.Gwendolyn: Harry, we must beware of these men. They are desperate characters.
Harry: What makes you say that?
Gwendolyn: Not one of them looked at my legs!
- Sleeping Single: Harry and Gwendolyn on the boat. Appropriate enough since Harry seems to have very little interest in his wife.
- Smart People Play Chess: Gwendolyn is very dramatic and given to flights of fantasy, but she's definitely much smarter than her dimwit of a husband, as shown in the early scene where she thrashes him at chess.
- Surprisingly Good English: The gang has been brought to a local officer after shipwrecking in Africa. Peterson launches into a very condescending talk in pidgin English trying to explain how they went from a "big boat" into a "small boat." After he finally says "Savvy?", the officer gives him a look of withering contempt and says "You will please to show me your passports."
- Sword Cane: Major Ross has one and he is about to make some holes in Harry when Billy arrives Just in Time.
- Tempting Fate: Harry, a former Navy officer, attempts to fix the boat's malfunctioning engine. He comes back up from below and announces "We may now proceed without further delay and in absolute safety." Immediately after this, a loud bang is heard from the engine room, and the purser barges in and says they're sinking.