Blind writer overhears two people in pub plotting to kidnap a child. But how to identify the potential kidnappers?
Decent but dumbed down and over-Americanized adaptation of Philip MacDonald's excellent 1938 novel Warrant for X, previously filmed in 1939 as The Nursemaid Who Disappeared. Making the main character blind is a cheap ploy that the novel did not need to resort to. The pacing is also very slow, which makes it a bit of a slog, as does each scene of obnoxious Yank Johnson talking down to British character actors (this is one of those films where all the police are dolts, but the hero is brilliant, because the scriptwriter was lazy). Good supporting cast, though, and the bones of MacDonald's novel make a decent framework to hang a suspenseful story on, however muddled the final results.
Note: The scene(s) with the Da Mestres appear to have been cut, or are at least not present in the exisiting print.