Justinian's Flea by William Rosen is an interesting book and well worth reading. You will learn more than you ever really wanted to know about the taxonomy of single-celled organisms, the operations of the gut of a flea, and the strong-minded actions of the Empress Theodora (and her good friend Antonina), whose resolve and tough-mindedness kept Justinian from fleeing the city when it looked as though the Blues and the Greens were going to send a successful usurper to the throne.

The section on Justinian's Civil Codex and its ramifications for current law is worth the price of the book alone. The chapter covering the building of the Hagia Sophia really got down to brass tacks (or rather uncured mortar and uncertain financing).

Though the work lags at times, mired in minutae, it is readable and interesting and a good secondary source for the history of the pivotal time at the end of the age of Antiquity and the beginning of Medieval times.

All because of a flea, the vector for the plague, history was warped from what seemed its certain course by the mid 6th century, so argues the author, quite convincingly.

I haven't finished the book, but you know how it ends anyway.