Bob and Jill Lawrence (Banks and Best) are a couple on holiday in Switzerland - until a man is shot in cold blood.
His last words speak of an assassination to take place in London and he needs the Lawrences to warn the British authorities.
Before they can, spies kidnap their teenage daughter in order to keep them quiet.
Now, forced to act alone, they must face the will of the evil ring-leader (Peter Lorre).
The final gun battle sequence was based on an actual event called the "Sidney Street siege" which occurred in London.
While this movie would be remade 22 years later (with Jimmy Stewart and Doris Day as the leads) many feel the 1934 version is the superior film; mainly due to Lorre's performance.