Professor Claus Eisenstadt, a refugee from Nazi Germany, and a brilliant mathematician, disappears from Columbia University one day. After the police have given up the search, mathematics graduate student Judy Carter, compelled to solve puzzling problems-both in science and in real life-becomes intrigued with his sudden disappearance. As she tries to learn more about the whereabouts and welfare of the professor, Judy begins to suspect his unexpected absence may have something to do with his earlier days in Germany. Judy follows up on some of her theories about Professor Eisenstadt's mysterious disappearance, but she is forced to give up without a solution.

Years later, Judy has herself become a professor. While on sabbatical in Germany, she decides to look further into Eisenstadt's disappearance, and begins to understand more about him, but is unable to find the answer to the puzzle of his vanishing. When Judy returns home to the US, she finds a thick envelope waiting for her, which contains an unusual request. She is surprised to find that it concerns Eisenstadt. Could this unexpected package be the link that helps Judy finally learn what happened to Claus and why he vanished?

As the story unfolds, the novel travels between student days in prewar Germany and postwar America, which were impacted by prewar anti-Semitism and postwar guilt. The reader is allowed a glimpse into the work of scientific researchers and the interplay of that work with their personal lives.