The Man Who Knew Too Much (1956)-tt0049470

 American tourists James Stewart and Doris Day are witness to the street killing of a Frenchman (Daniel Gelin) they've recently befriended. Before breathing his last, the murder victim whispers a secret to Stewart (the Cinemascope lens turns this standard closeup into a truly grotesque vignette). Stewart knows that a political assassination will occur during a concert at London's Albert Hall, but is unable to tell the police: his son (a daughter in the original) has been kidnapped by foreign agents to insure Stewart's silence.

The Lady Vanishes (1938) -tt0030341

The Lady Vanishes, Alfred Hitchcock's comedy-thriller, came at the end of his British period;  The film concerns the young Iris Henderson (Margaret Lockwood), heading home on a train after spending the holidays in the Balkans. Iris becomes friends with a kindly old lady, Miss Froy (Dame May Whitty) after Iris gets hit in the head with a flowerpot meant for Miss Froy. On the train, recovering from the blow, Iris falls asleep. When she awakens, Miss Froy has vanished, replaced by someone else in Miss Froy's clothing. Iris talks to the other passengers, a bizarre collection of eccentrics who think that Iris is crazy for insisting on there even being a Miss Froy -- everyone denies having ever seen the old woman. Finally, Iris finds a young musician, Gilbert (Michael Redgrave), who believes her and the two proceed to search the train for clues to Miss Froy's disappearance. 

Secret Agent (1936) -tt0028231

British soldier and novelist Edgar Brodie returns home during WWI to find that a government agency has faked a report of his death. They get him to change his name to Richard Ashenden and travel to Switzerland to track down a German agent.