In this story set in a futuristic Utopian society, a boy named Gemm is labeled a deviant. Viewed as a threat to his society, Gemm is told he must undergo a mysterious cure or both he and his twin sister will be recycled. When Gemm chooses to take the cure, he is transported back in time to the year 1348--at the onset of the Black Plague. Gemm, now a Jewish 16-year-old named Johannes, finds himself living in Strasbourg, a town rife with anti-Semitism. As Gemm/Johannes struggles to preserve his religious faith, he must also confront the horrors of the plague.