The lifeline - Phyllis Bottome

Mark Chalmers, 36, dark haired, athletic, keen on skiing and winter sports, speaks fluent French and German and has a taste for wine, food and women. Sounds familiar?
It is 1938, pre the Munich Agreement and post Anschluss. Chalmers, a master at Eton, is recruited by an old friend at the Foreign Office and introduced to his boss 'B'.
Chalmers reluctantly agrees to take on a hazardous mission for British Intelligence - to parachute into Nazi-occupied Austria and pass on information to a British agent.
In case of trouble he is given a suicide pill. Chalmers has no intention of committing himself beyond this one job but once he reaches his destination, he finds himself sucked into the cause fighting fascism with the Austrian-German Underground - until there is no turning back.