Yul Brynner (yes, Yul Brynner, believe it or not) plays a U.S. Secret Service agent assigned by Washington to investigate an international gang counterfeiting $100 bills in Europe. He teams up with a Scotland Yard detective played by Edward Woodward ("The Equalizer" in a future life).
The movie opens with the gang attempting to assassinate Brynner near the United Nations building in New York, because he has developed too much evidence. The gang misses, of course, but his girl friend is killed. Brynner travels to London, works undercover, and gets in good with the gang.
I gave this movie a 7 out of 10, if only because they got the right American law enforcement agency (Secret Service) investigating counterfeit.