As a mortal woman in medieval Yorkshire, Marion Chase falls in love with a young woman and is shunned by the church and the village. Marion takes refuge in a forest cottage and becomes an herbal healer. When men from the village threaten to burn her as a witch, Marion is rescued by a vampire, transformed, and joins a Sisterhood in York dedicated to ethical living for vampires. When Henry VIII's 1546 ban on prostitution reaches York, the Sisterhood closes its brothel and disbands. The vampires scatter and Marion becomes a battlefield nurse travelling throughout Europe.

She travels to America during the Civil War and is then instrumental in the development of blood banking in the 1930s. In the 21st century Marion runs a Chicago blood bank with a hidden sideline of providing ethically sourced blood to Midwestern vampires. All is well until Marion falls in love with the one person who can destroy her. Rachel Sutter is an FDA inspector who is the living likeness of Marion's medieval love.