Tess, who is estranged from her husband and her family, discovers an ancient scroll while working at an archaeological dig for the National Geographic. Instead of turning over her spectacular find to the association, she hides it, thinking that its potential value could be her answer to financial independence for the rest of her life.

She spirits the scroll out of Turkey into Italy, where she starts to decipher the parchment in a squalid flat in Rome. She discovers that the document recounts the lives of Aquila and his wife Prisca. Aquila had been present in Jerusalem during the crucifixion of Jesus and became an ardent convert to the Christian faith. Prisca was the daughter of a wealthy Jewish merchant, who, because of duplicity and amazing bad fortune ends up a slave to a vicious Roman master. Aquila had known and loved Prisca before disaster befell her and her family, and is reunited with her after she escapes her vile master.

Aquila baptizes Prisca and the rest of their story revolves around their travels throughout the ancient world, spreading the word of their new God and meeting and working with the likes of St. Peter, St. Paul, and Mary, the mother of Jesus. As Tess works her way through the translation, she experiences a change of character so dramatic that it almost explodes in the conclusion of the novel.