The novel concentrates primarily on the alien encounter in the 14th century, paying special attention to the interplay between Dietrich, a Christian scholar who is fond of Aristotle and metaphor, and the technologically advanced, post-Einsteinian band of otherworldly travelers. The interplay includes two theological questions. The first, "can aliens become Christians?" is answered in the affirmative, as some of them become converts. The second, "where is God when things go wrong?" is more difficult to answer, for both the Germans and the alien Krenken. The Germans are stricken by the Black Death, and the Krenken, who are immune to the disease, but cannot return to their home, require an amino acid not found in earthly organisms. The answer is two-fold: there is always hope, and God's love is expressed to us in the unselfish love of fellow creatures. Dietrich's attempts to understand the science of the Krenken (their view of the solar system, and gravity, is quite different from his) and their attempts to explain it to him, are also an important theme.