Secret Venture (1955)

Professor Henrik, a world-famed scientist who holds the secret formula for a new type of jet fuel, returns to England, and his briefcase is switched with that of Ted O'Hara. Henrik is met by his secretary , Joan Butler, but when she is called away Henrik is kidnapped by a gang, headed by a man called Zelinsky. O'Hara becomes acquainted with a Renee L'Epine, who unknown to him, is a member of Zelinsky's gang. She and Squire Marlowe take O'Hara, against his will, to Zlinsky's headquarters, and it is disclosed that they KNOW he has Henrik's briefcase---which is more than he knows---and are willing to pay him a considerable sum of money for it. O'Hara gets in touch with Scotland Yard Inspector Dalton and O'Hara tells Dalton that the name of Weber, an espionage agent, was mentioned by Zelinsky. The Inspector tells O'Hara to take the formula to Weber in Paris to negotiate with him. On the boat-train Renee and Dan Flemying take the formula from O'Hara and, arriving at Weber's establishment and have already handed it over to Otto Weber), but they didn't have the code. A few days later, O'Hara follows Joan to Trafalgar Square, where he sees her hand something over to Marlowe...and, thusly, the plot thickens