Also known as "In Our Hands, the Stars", this book has equal elements of speculative science fiction, international espionage, and cautionary tale about the misuse of science and habits of security.
Basic plot synopsis - A top Israeli scientist discovers something that will revolutionize travel both here and in space, and returns to his native Denmark for reasons revealed later in the book. Other nations (primarily cold war America and Soviet Union) try to acquire this technology, providing much of the tension and the climax of the novel.
I couldn't put this book down. The speculative science was spot on, the paranoia of the other governments was an excellent adversary. I especially enjoyed the touches of humor. While on Mars, the two main characters have a moral discussion of scientific responsibility and the actions of Denmark during World War II which is particularly well done.