Caleb Levi, former college basketball star turned history professor, is back for his sixth summer of research in Florence, Italy. While there he translates the reports of Niccolo Nannrone, a 15th century spy who served a politically ambitious cardinal, and learns of nefarious plots and brutal murders in the late 1400s. Then one day, to his great surprise, Caleb witnesses a death in the 21st century that mimics one he had just read about in Nannarone's latest report.

Against his better instincts, Caleb looks into a possible connection between those two deaths some 500 years apart. He has...