Striking similarities and differences from MacInnes' prior two World War II espionage novels (I exclude her pre-war husband and wife spy story) emerge in this tale set mainly in the Southern Tyrol. It covers a period in time from September 1943, when the Italians have just signed an armistice with the Allies, to May 1944. British Infantryman Peter Lennox and other POWs break out of a prisoner of war camp that had been run by the Italians. The Italian guards melt away, but the POWs must fight their way through a newly arrived German convoy carrying as prisoners Allied officers. Already, the reader can sense the action to come. MacInnes has shaped a fast moving novel that, while it doesn't eradicate it entirely, does pare down the lengthy passages of introspection and, yes, gloom that seemed to inhabit the earlier works. As a result, Horizon is a much shorter work, too. Peter Lennox's story of escape to the Tyrol barely has time to let you get your breath. And I, for one, all the way through kept seeing parallels with the Frank Sinatra film, Von Ryan's Express.
Comparisons with film cease, however, upon arrival in Hinterwald, the Tyrolean village where Lennox has been sent to prepare the way for Allied organizers who will help set up resistance to the Germans. Two things. First, MacInnes' focusing on this obscure and mostly forgotten arena of World War II is founded in fact. There was indeed a South and North Tyrolean resistance to the Nazis who hoped to see an independent Tyrol after the war. In this the Allies betrayed them, of course, giving this German speaking region back to the Italians, where it became a source of some international friction and even terrorism until the early 1970s. Second, Hinterwald is the perfect setting for the now tried and true MacInnes forumula for spy fiction: an Allied soldier (lost behind the lines); an agent, or Lennox the escaped POW finds himself caught up in rustic isolation. A middle aged woman in charge of her isolated wartime house provides scarce food and clothing, while the soldier whiles away his time reading books, writing/painting, philosophizing, and going stir crazy and fearing exposure to the Germans, until interaction with a young local woman leads to an explosion of action and fighting at the end.
All in all, a good workable plot. MacInnes seems to have learned a great deal between novel number three and this one. She still has her fine eye for detail and atmosphere, but each and every step of the way in Horizon she has learned to advance the story. No wasted pages or passages. Superb.