The Enterprise of Death by Jesse Bullington

Goodreads Storygraph

"As the witch-pyres of the Spanish Inquisition blanket Renaissance Europe in a moral haze, a young African slave finds herself the unwilling apprentice of an ancient necromancer. Unfortunately, quitting his company proves even more hazardous than remaining his pupil when she is afflicted with a terrible curse. Yet salvation may lie in a mysterious tome her tutor has hidden somewhere on the war-torn continent. She sets out on a seemingly impossible journey to find the book, never suspecting her fate is tied to three the artist Niklaus Manuel Deutsch, the alchemist Dr. Paracelsus, and a gun-slinging Dutch mercenary. As Manuel paints her macabre story on canvas, plank, and church wall, the young apprentice becomes increasingly aware that death might be the least of her concerns."