Based on Eric Ambler's novel The Light of Day, it tells of Arthur Simpson (Ustinov), a jack-of-all-trades and small time con artist who gets roped into helping a group of international art thieves headed by Elizabeth Lipp (Mercouri) to steal an emerald-studded dagger from İstanbul's Topkapi Palace, while he's simultaneously forced to spy on them for the Turkish Secret Police.
The jeweled "Topkapi dagger" that the gang wants to steal is real.
This film provides examples of:
- The Caper: A plot to steal a priceless dagger encrusted with diamonds and four enormous emeralds.
- Con Men Hate Guns: He's a thief, not a con man, but it's basically the same thing. When plot developments result in a change of plan, where the gang will slow down the roving spotlight instead of Walter shooting it out, Walter is pleased.Walter: I never liked that gun. It upset the artist in me.
- Diabolus ex Machina: "A little bird told me." The intricately planned heist goes wrong because a bird, which flew in through the window just before the thieves closed it, alights on the floor of the museum, triggering the alarm.
- Face Framed in Shadow: Only Elizabeth's eyes are visible as she turns in poorly-lit Topkapi Palace to the viewer and says "I'm a thief." Then the lights flip on to illuminate her whole face as she says "Honest."
- Glasses Pull: Major Tufan, who has worn his Sinister Shades throughout the film, takes them off to deliver his "A little bird told me" line, telling the gang that the jig is up.
- Here We Go Again!: The movie actually ends with these words, as the protagonists plan another caper while still in prison.
- Hidden in Plain Sight: The dagger is smuggled away by being put on a wax dummy of Mahmud I just like the one in the museum, with the dagger pinned to the wax dummy's tunic just like in the one in the museum, as if it were costume jewelry.
- Honest John's Dealership: Simpson sells fraudulent antiques to tourists and offers to show them the local nightlife (in the novel, it's explained he has an arrangement with local prostitutes wherein they rob customers he sends their way and share the proceeds with them).
- It's Not Porn, It's Art: Simpson lost his British citizenship because he was caught smuggling pornography. When questioned about it by the Turkish secret police, he handwaves that by citing the recently unbanned Joyce (presumably Ulysses) and Lady Chatterley's Lover.
- Lighter and Softer: Compared to the original novel, in which Simpson is more of a Dirty Coward and has engaged in more villainous actions.
- Lovable Coward: Arthur is one, and actually convinces the Turkish secret police to trust him by monologue on how from looking at him, they should know he would never be involved in terrorism.
- "Mission: Impossible" Cable Drop: The original. The Trope Namer is actually a homage to the one in this movie.
- Money Fetish: Ms. Lipp has one, or more precisely a jewelry fetish.Elizabeth: The emerald excites me, physically, like a man.
- No Fourth Wall: Elizabeth tells her own story, addressing the camera directly.
- Obfuscating Stupidity: While Simpson isn't that bright, he's smarter than both the criminals and the Turkish police think he is.
- Plucky Comic Relief: Simpson plays this role in the band of criminals, although oddly, he's the protagonist.
- Separated by a Common Language: Actually, they aren't separated by a common language, but this is still played for a gag when the two Brits, Simpson and Page, meet in Istanbul.Page: I suppose you want remuneration, like everyone else.
Simpson: Well there was the gasoline, sir.
Page: The gasoline? [realizes] Oh, you mean petrol.
Simpson: I thought you might be an American gentleman, sir.
Page: [horrified] No.
- Sinister Shades: Major Tufan, the head Turkish wears completely opaque lenses to creepy effect.
- Through the Ceiling, Stealthily: The Caper, when our heroes dangle themselves into the room to steal the dagger without touching the floor and triggering the alarm. Also how it's undone as a bird flies in the window during the "Mission: Impossible" Cable Drop and sets off an alarm before the villains have made their getaway.
- Video Credits: The film ends with the names of the primary actors popping up onscreen, as the gang of thieves walks into the Kremlin, plotting their next heist.