Undercover agent Robert Leyland entraps crooks trying to sneak expensive goods past customs on transatlantic crossings. After Leyland falls for reluctant smuggler Barbara Standish, he convinces her to return with him to France with her cache of diamonds. But she is unaware of a network of thieves onboard their ship, competing against each other to make off with her jewels.
| Actor | Role |
|---|---|
 James MasonRobert Leyland | Robert Leyland |
| VViki DobsonBarbara Standish | Barbara Standish |
| EEddie Pola'Terrible' Tony Canzari | 'Terrible' Tony Canzari |
 Finlay CurrieAl Parson | Al Parson |
| JJohn WarwickEddie 'Babyface' Fallon | Eddie 'Babyface' Fallon |
 Margaret Rutherford'Crafty' Maggie Carberry | 'Crafty' Maggie Carberry |
| PPaul BlakeCornwallis | Cornwallis |
| JJames MageeanBen | Ben |
| EEva HudsonManzanilla | Manzanilla |
| PPaul SheridanFournival | Fournival |
| PPeter PoppBertram Plush | Bertram Plush |
| BBernard MerefieldMr Lowry, Ship's Purser | Mr Lowry, Ship's Purser |
| CCharles SewellShip's Captain | Ship's Captain |
| ZZoe WynnLenore Kendall | Lenore Kendall |
| JJack LesterSuperintendent Welbekker | Superintendent Welbekker |