Having made her way up from Spain to France and left (she hopes!) her life as a prostitute behind her, the half-Scottish half-Spanish Mariana de la Mar (Marian MacElpin) is now an unofficial student at the university in Paris. Unofficial, because women are not admitted to lectures, so she has to pretend to be a man. But it is to her that the other students turn when one is charged with the murder of his rich uncle, a miser and reputed alchemist.
Mariana quickly discovers that the murder (and a second related murder) had their roots far away on the island of Ibiza eighteen years earlier, and involve not only alchemy and the tarot and (of course, with Mariana there) witchcraft (one of the witches, known as La Fille d'Or, turns out to have been for years the secret mistress of Charles VI, King of France), but also a one-armed Albanian "king" of the Paris underworld, and such well-known historical figures as Christine de Pisan (then a girl of thirteen), and Nicolas Flamel.