The absolute best historical/alternative history fiction I have ever read, bar none, is “The Dragon Waiting” by John M. Ford. Mike was one hell of a writer an this was him at his best.

amazon.com

The Wars of the Roses have put Edward IV on the throne of England, Lorenzo de’ Medici’s court shines brilliantly, and Duke Galeazzo Maria Sforza plots in Milan. But this is a changed world, and medieval Europe is dominated by the threat from the Byzantine Empire. Sforza, the Vampire Duke, marshals his forces for his long-planned attack on Florence, and Byzantium is on the march. A mercenary, the exiled heir to the Byzantine throne, a young woman physician forced to flee Florence, and a Welsh wizard, the nephew of Owain Gly Dwr, seem to have no common goals but together they wage an intrigue-filled campaign against the might of Byzantium, striving to secure the English throne for Richard, Duke of Gloucester, and make him Richard III

So many wonderful what ifs - what if Byzantium stayed strong because what if magic were real? What if vampires were the result of a disease? What if Christianity did not replace the old religions but was simply a tiny one of many? What if Richard were a good guy? And so on.

If you like alt history, this one is not to be missed.