Essentially a film version of China Smith television series (1953-1954), for which Lindsay Hardy also wrote, about an Irish conman and adventurer operating in Singapore (series one) and then Hong Kong and Macao (in series two). This film used the same production studio, sets, and cast members as China Smith, but re-named the characters.
Like China Smith, Mike Callahan is an Irish soldier of fortune who, in this film, thwarts the attempts of an international gang to kidnap an eminent nuclear physicist for ransom.