The Black Bag.

Billy Kirkwood, a young businessman, travels to New York City for a vacation. There he comes to the rescue of pretty young Dorothy Calender, escorting her to a taxi because she was being followed by some sinister-looking men. It turns out that the men are thieves who have seen her take an expensive diamond necklace from a store, and are following her to steal it. However, all is not quite as it seems, as Billy is soon to find out.