On 9th April 1940 when the Germans invaded Norway, many of the officers who were at the spearhead, were men who as teenagers in the First World War, were evacuated from Vienna to escape the Italian bombing, to stay with kindly and hospitable Norwegian families. They were especially chosen because they possessed an unusual intimate knowledge of the Norwegian people, their country and their language, It was Winston Churchill who gave them their contemptuous name "Vengeful Cuckoos" returning to foul the very nests that had once given them loving sanctuary.
This is the story of one of them, Kapitan zur See Otto Wilhelm Schmidt, 38, a German naval officer, in command of "Essen" a destroyer converted as a mine layer, ordered to return to Haeranger, a small fishing town on the edge of a fjord in Southern Norway, ordered to act as civil administrator until such times as the occupation is complete when specially trained personnel will take over.
Wilhelm believes the occupation of Norway is to protect the people from the aggressive British plans to invade Norway and is determined the occupation of Haeranger will be as peaceful as possible. This does not meet with the approval of Oberleutnant Fritz Goetz, his second in command, who is arrogant, overbearing and secretly a member of the Abwehr, the German military intelligence. Wilhelm despises Goetz and the Nazi party that has produced him and others like him.
He formally presents himself to the Mayor of Haeranger, and is shocked when he discovers the man with the gold chain of office is Jon Hermansen, the head of the family who kindly took him in as an evacuee, and his daughter Kristin with whom he had a youthful romance, is now a poised and beautiful women, and is acting as Deputy mayor as her mother had sadly passed away.
Suddenly torn between his duty to the Reich and his desire not to deal too harshly with the people as disobedience and the resistance grows, Wilhelm is forced to adopt stronger and oppressive measures, including Kristin and her family.
In the midst of the turmoil, Kristin breaks certain news to Wilhelm that propels him into a decision where he has to seek the help of the resistance.
An elaborate, but risky plan is put into place by the resistance and as a consequence Wilhelm finds himself being gradually overwhelmed by the developing situation until it reaches a surprising and dramatic climax.