Die Eroberung der Zitadelle (1977)

While on an automobile tour of Italy with his mother, the German publisher in this story has an accident which results in her death. He decides to stay and look for work in Italy, rather than return to his responsibilities, and takes a job working on a construction site. His co-workers are similarly displaced men: one is a Greek exile, the other a Basque terrorist. The elaborate house they are working on is to be the home of a wealthy local man.