Sherlock Holmes in Washington (1943)

Sherlock Holmes is engaged by the Home Office to locate a British subject traveling for his law firm to Washington, D.C. The man had flown to New York City and then took the train to Washington. On the outskirts of the city, the man was kidnapped and has not been seen for several days now. Holmes learns from the Home Office that the man was in fact a government agent who was delivering a highly secret, two page document to the US government. In verifying the contents at his flat, Holmes concludes the document had been reduced to microfilm. The question becomes whether he may have had the opportunity to pass the microfilm to someone else on the train before he was taken.