The Fifth Essence

Why did a chemistry professor write a text on a medieval practice from the viewpoint of a practitioner? And why would a chemist for a suntan lotion company take such an interest in that professor and her hobby three and half decades later? Finally, and most important, why did they both vanish and where did they go? That was what Miami Beach private detective Nicholas Pierce was trying to figure out when he realized that it was no coincidence that two police detectives investigating the case had been found dead.