Roxanna. The Fatal Secret of the Murder Books

It begins with a murder, as befits a detective story, a somewhat bizarre female detective, events that take place in Rome, England and France. A story that jumps back to the Middle Ages, runs on two tracks, two suspicious women and a dead man who suddenly appears one night to one of the two suspects. Alive, of course, at least for a short time. Murder motives that don't want to reveal their secret and the simultaneous death of both suspects who, to make matters worse, are absolutely the only ones who could be responsible for the crimes.
A tangled criminal string that seems to have been partially untangled by diligent endeavors, only to become even more tangled in the next moment and finally, seemingly lying in front of you untangled in a perfectly straight line.