Catherine Neal, an intelligent, educated young girl, suddenly agrees to a modest position as a secretary-assistant for an elderly Scottish lady. This raises legitimate suspicions among the grandson of the owner, who is engaged in serious scientific research in the field of medicine. Stephen wants to keep his discovery a secret for now, and his grandmother's new secretary takes a keen interest in his affairs, eavesdrops on conversations and writes something down in her notebook all the time. Then he begins to follow Katherine......