The Lost Chart — Neil M. Gunn

At the height of the cold war, shipping executive Dermot Cameron is entrusted by British Intelligence with a chart of the approaches to a remote but strategically important Hebridean island. Rescuing a young woman from two attackers in the street, he becomes involved in a brawl and loses the chart. His subsequent hunt for the lost chart leads him into adventures on land and sea, and involves him in brushes with a murderous communist fifth-column. As a diplomatic crisis looms, bringing with it the threat of a potential nuclear showdown between the super-powers and a return to the dark ages, Dermot's search prompts his own personal reappraisal of the people and things he values.