Written and produced by Norman Swallow.
This film tells the story of the medical officers of the Port of London Health Authority who stand on guard as the first line of defence against infectious diseases.
A ship comes from Asia, heading for the Channel. One of the passengers is sick. 'Query smallpox' is the message sent by the ship's surgeon. In thirty-six hours the ship will be in London, capital of a country of fifty million people, only a quarter of whom are vaccinated.

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